





*'p^ 







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THE SCIENCE OF HUMAN BEHAVIOR 



THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO 
DALLAS • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY • CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



THE SCIENCE 



OF 



HUMAN BEHAVIOR 

BIOLOGICAL AND PSYCHOLOGICAL 
FOUNDATIONS 



BY 

MAURICE PARMELEE, Ph.D. 

UNIVERSITY OF MISSOURI 

AUTHOR OF "THE PRINCIPLES OF ANTHROPOLOGY AND SOCIOLOGY 
IN THEIR RELATIONS TO CRIMINAL PROCEDURE," ETC. 



THE MACMILLAN COMPANY 
1913 

All rights reserved 



/ 



T3 



Copyright, 191^, 
By THE MACMILLAN COMPANY. 

S«t up and dectrotyped. Published January, 1913. 



KortooolJ Tl^rnn 

J. 8. Coflhtng Co. — Berwick «k Smith Co. 

Norwood, Mass., U.S.A. 









XTo 

THREE MASTER INVESTIGATORS 

JACQUES LOEB • H. S. JENNINGS 
CHARLES S. SHERRINGTON 

EACH OF WHOM HAS IN HIS OWN WAY DONE MUCH 
TO ADVANCE THE SCIENCE OF BEHAVIOR 



PREFACE 

The study of human phenomena must be carried on 
largely through the psychological and social sciences. 
Much of the writing in these sciences still consists of vague 
generalizations which have not been subjected to the test 
of being appHed to a large number of data. What is 
needed above all is to carry much further the painstaking 
labor of accumulating a large mass of facts from which 
generalizations can be safely deduced. In other words, 
these sciences must get down to concrete realities more 
than they have in the past if they are to develop on a 
stable basis. 

It is the fimction of every science, on the one hand, to 
reduce as far as possible the phenomena with which it 
deals to the terms of the science upon which it is based, 
and, on the other hand, to describe the peculiar character- 
istics of these phenomena which distinguish them from the 
phenomena out of which they have evolved and which 
make them a fit subject for treatment by a distinct science. 
Thus psychical and social phenomena should be reduced 
as far as possible to biological terms, just as vital 
phenomena should be reduced as far as possible to 
chemical and physical terms. On the other hand, the 
peculiar characteristics of psychical and social phenomena 
should be described, just as the pecuHar characteristics of 
vital phenomena should be described. Thus, on the one 
hand, the continuity of the evolutionary series would be 



viii Preface 

shown, while, on the other hand, would be illustrated the 
creative nature of the evolutionary process which is ever 
bringing into being new combinations of matter and 
energy or whatever the ultimate elements of the universe 
may be. 

If then the psychologists and social scientists place 
their work more than ever on a biological basis they will 
make it more definite and concrete and will get much nearer 
to the real nature of the phenomena with which they 
deal. In this book I have brought together the results 
of recent work in biology in general and in zoology and 
neurology in particular, in genetic and comparative psy- 
chology, and in anthropology, and have tried to show the 
significance of this work for the analysis of human be- 
havior. The book contains certain contributions which 
will, I hope, be of interest to psychologists, anthropolo- 
gists, and social scientists. But I hope'it will be of value 
also to many general readers who will be glad to have in 
convenient form the results of this work which is of so much 
significance for the study of human behavior and human 
nature. It should be useful to those engaged in educa- 
tional work and may also prove to have utility as a college 
and university textbook in certain courses in psychology 
and sociology, as, for example, courses in comparative psy- 
chology and in biological and psychological sociology. 

While a single theme runs through this book, namely, 
the evolution of behavior, yet the book naturally falls into 
several parts, each of which may be read with some profit 
apart from the rest. Chapters II to IV summarize most 
of the fundamental facts and principles of modem biology. 
Chapters V to VII describe briefly the behavior of the lower 
animals. Chapters VIII to X give some of the most im- 
portant facts and principles of neurology. Chapters XI 



Preface ix 

to XVI cover the whole field of psychology in a concise 
fashion and, in fact, form in themselves a small treatise on 
psychology. Chapters XVII to XX state the most im- 
portant facts with regard to the beginnings of social evo- 
lution and the fundamental forces in social evolution. 

This book is the first of a series of works in which I 
propose to deal with the evolution of human culture and 
of human nature on the basis furnished by this book. 

I wish to thank my colleagues in the University of 
Missouri, Professors W. C. Curtis, D. H. Dolley, C. A. 
Ellwood, J. W. Hudson, George Lefevre, and Max Meyer, 
each of whom has read one or more of the chapters and 
has o£fered comments and criticisms thereon. 

I wish also to thank the following pubhshing firms, 
P. Blakiston's Son and Company, The Columbia Uni- 
versity Press, Henry Holt and Company, and J. B. Lip- 
pincott and Company, each of which has given me 
permission to use illustrations which have appeared in 
books published by it. 

MAURICE PARMELEE. 

December, 1912. 



PAGE 



CONTENTS 

CHAPTER I 
THE STUDY OF BEHAVIOR 

Definition of behavior — The science of behavior in relation to bi- 
ology, psychology, and sociology — The genetic method of study — 

— Plan of this book 1 

CHAPTER II 

THE PHYSICO-CHEMICAL BASIS OF BEHAVIOR 

Physical and chemical characteristics of matter — Reasons for the 
mobile and plastic character of organic matter — The origin of the 
organism — The cell — The constituents of organic matter . . 7 

CHAPTER III 

THE ANATOMICAL AND PHYSIOLOGICAL BASIS OF 
BEHAVIOR 

MetaboHsm — Respiration — Circulation — Reproduction — Sex — 
Theories of the origin of species — Orthogenesis — Nageli — Eimer 

— Differentiation of species through the action of external forces — 
Lamarck — Adaptation through the transmission of acquired char- 
acters — Darwin — Variation — Selection — Criticisms of Darwinism 

— Weismann — Inheritance through the germ cell — Germinal selec- 
tion — Panmixia 20 

CHAPTER IV 

THE ANATOMICAL AND PHYSIOLOGICAL BASIS OF 
BEHAVIOR {Continued) 

Heterogenesis — Discontinuous variations — Bateson — Substan- 
tive and meristic variations — Symmetry — De Vries — The mutation 
theory — Micromeric theories of the germ cell — Unit characters — 
Mendel — The Mendelian law of inheritance — Dominant and reces- 
sive characters — The segregation of allelomorphic characters — 
Homozygotes and heterozygotes — The Mendelian explanation of 
particulate, exclusive, and blended inheritance — Reversion or ata- 

zi 



xii Contents 



?AGB 



vism —r Galton's laws of ancestral inheritance and of filial regression 

— Mendelian criticism of Galton's laws — Statistical and physiological 
laws of inheritance — The exaggerated claims for Mendelism — Jo- 
hannsen's theory of pure lines — Sex determination — Sex as a unit 
character — The biological basis for psychology, anthropology, and 
sociology 45 

CHAPTER V 

THE BEHAVIOR OF THE LOWER ANIMALS 

Behavior as the dynamic, functional aspect of external organic 
phenomena — Application of the genetic method in psychology — 
The genetic method as the phylogenetic method — The develop- 
ment of the science of behavior by biologists and comparative psy- 
chologists — Experimental psychology — The irritability of organic 
matter arising out of its unstable and mobile nature — Is this irrita- 
bility a psychic characteristic? — The direct reactions of organisms 
to external forces — Definition of a tropism — The external forces 
which act upon organisms 75 

CHAPTER VI 

TROPISMS 

Photo tropism — Photopathy — Does the direction or the intensity 
of the rays of light determine the reactions of organisms to light? — 
Positive and negative phototropism — Is the action of light on organic 
matter mechanical or chemical? — Chromotropism — Rudimentary 
vision — The utility of reactions to light — Geotropism — The force 
of gravity — Chemotropism — Rudimentary senses of smell and taste 

— Galvanotropism — Barotaxis — Stereotropism (thigmotropism) or 
contact irritability — Rheotropism — Anemotropism — Thermotro- 
pism — Hydrotropism — Tonotropism 88 

CHAPTER VII 
THE EVOLUTION OF ANIMAL BEHAVIOR 

Determination of behavior by form and past experience and by 
external stimuli — Description of the behavior of Amoeba, Parame- 
cium, Stentor, etc. — The action system — The reflex — The physio- 
logical state of the organism as a factor in the determination of be- 
havior — The regulation of behavior — The development of behavior 
in the race — Organic selection — The laws of animal behavior 117 



Contents xiii 

CHAPTER VIII 

THE EVOLUTION OF THE NERVOUS SYSTEM AND 
THE REFLEX ACTION 

PAGE 

Progressive increase in the self-determination of behavior — Nerve 
cells and fibers — The specific qualities of nervous matter — Defini- 
tions of the reflex action — Receptor, adjustor, and effector organs 

— The simple reflex action — The conductibility of nervous matter 

— The adaptive character of reflex actions — The origin of the nerv- 
ous system — The appropriation of effectors by the nervous sys- 
tem — The selective excitability of receptor organs — The neurone 

— The connections between the neurones — The central nervous 
system 137 

CHAPTER IX 

THE FUNCTIONS OF THE NERVOUS SYSTEM 

The kinds of reflex arcs — Facilitation — Inhibition — The common 
path — The integrative function of the nervous system — Mechanical, 
chemical, and nervous integration — The functional divisions of the 
nervous system — The origin of the head and brain — The functions 
of the distance receptors — Extero-ceptive, proprio-ceptive, and 
intero-ceptive receptors — The neuromeres — The divisions of the 
brain — The functions of the cerebellum — The functions of the cere- 
brum — The divisions of the cerebrum 158 

CHAPTER X 

CEREBRAL LOCALIZATION 

Phrenology — Anatomical study of cerebral functions — The anat- 
omy of the brain — White and gray matter — The cerebral cortex — 
Theories of cerebral localization — The association areas — The 
cerebral fibers — Physiological study of the cerebral functions by 
stimulation and extirpation — Clinico-pathological study of cerebral 
functions — Functional and organic diseases of the brain . . . 175 

CHAPTER XI 

THE NATURE OF INSTINCT 

Mistaken conceptions of instinct — Instincts as congenital tenden- 
cies to action — The relation of instinct to tropism and reflex action 

— The adaptive nature of instincts — The structural basis of instincts 



xiv Contents 



— The hereditary nature of instincts — Instincts as characterizing 
species — The degree of permanency of instincts — Variations in in- 
stincts — Reenforcement and inhibition — Combinations of instincts 

— The degree of perfection attained by instincts — Instinct and con- 
sciousness — The relation between instincts and emotions — Defi- 
nitions of instinct — An instinct as an inherited combination of re- 
flexes 197 

CHAPTER XII 

THE NEURAL BASIS OF INSTINCT 

The cerebrum and instinct — The cerebellum as the principal nerv- 
ous mechanism for instincts — Localization of instincts in the spinal 
cord, medulla, and cerebellum — Impulsive instincts — Chain in- 
stincts — Analysis of the nesting instinct of soHtary wasps . . 227 

CHAPTER XIII 

THE PRINCIPAL HUMAN INSTINCTS AND GENERAL 
INNATE TENDENCIES 

The number of human instincts — The directing of instinctive tend- 
encies by intelligence — Description of the principal human instincts 

— The classification of the instincts — The nature of a general innate 
tendency — Imitation — Suggestion — Sympathy — Play — Emulation 

— Workmanship — Gregariousness — Habit 238 

CHAPTER XIV 

THE NATURE OF INTELLIGENCE 

Psycho-physical processes — Introspection — Intelligent behavior 
as the result of experience — Associative memory as a criterion of 
intelligence — Unspecialized nervous tissue essential for intelligence 

— The cerebral cortex as the neural basis for intelligence — The 
central nervous system as the organ of memory — The range of intel- 
ligence in the animal world — The structural advantages of the ver- 
tebrate for the development of intelligence — The reasons for man's 
superior intelligence — The nature of learning — Sensations — Im- 
ages — Memory — Sensori-motor and ideo-motor action — Pleasure 
and pain as reenforcing and inhibiting ideo-motor action — Ideas — 
Thought as a flow of ideas — Concepts as generalized images — 
Imageless thought — Reason — The nature of human intelligence . 256 



Contents xv 

CHAPTER XV 

CONSCIOUSNESS : SENSATION, ATTENTION, FEEL- 
ING, PLEASURE, PAIN, AND EMOTION AS 
CONSCIOUS ELEMENTS 

PAGE 

Spiritual conceptions of consciousness — Consciousness as charac- 
terizing all matter — Consciousness as characterizing all organic 
matter — Consciousness as an epiphenomenon — Consciousness as 
associative memory — The neural basis of consciousness — The rela- 
tion between intelligence and consciousness — Sensations as the raw 
material for consciousness — The nature of attention — The nature 
of feeling — Pleasure and pain — Feelings as pleasurable and pain- 
ful sensations — The neural basis of feelings — Feelings of pleasant- 
ness and unpleasantness — The nature of emotion — The visceral 
and vaso-motor origin of emotions — Emotions as affective sensa- 
tions or feelings 281 

CHAPTER XVI 

PERSONALITY, INTELLIGENCE, CONSCIOUSNESS, 
AND THE NATURE OF MIND 

Self-consciousness or personality based upon the integrated per- 
manent psychic elements — Self-consciousness as an idea — Multi- 
ple personality — The nature of voHtion — Subjective and objective 
aspects of consciousness — The relation between consciousness and 
intelligence — The criterion of consciousness — The functions of 
consciousness — Consciousness as self-consciousness — Definition of 
consciousness — Psycho-physical paralleHsm — Psycho-physical inter- 
actionism — Definition of mind — Mind as including intelligence and 
consciousness — Mental processes determined by minute physiologi- 
cal processes — Mfnd as a stage in the determination of certain 
kinds of behavior — The relation between mind and matter — The 
criterion of mind — Is our knowledge of mind subjective or 
objective? 307 

CHAPTER XVII 

THE BEGINNINGS OF SOCIAL EVOLUTION 

Definitions of association and society — Colonial species — Is there 
an inborn associative tendency ? — The external, environmental forces 
for association — The degree of correlation between organic and 
social evolution — Internal forces for association — Inborn and ac- 
quired characteristics 327 



xvi Contents 

CHAPTER XVIII 
INSECT SOCIETIES: THE ANTS 

PAGB 

Anatomical polymorphism — Physiological division of labor — The 
philoprogenitive instincts — The founding of an ant community — 
The food-procuring activities — The hunting stage — The agricul- 
tural stage — Harvesting — The pastoral stage — Symbiosis — Para- 
sitism — Myrmecophilism — Commensalism — Slave-making — The 
intelligence of ants — The ant brain — Recognition — Communica- 
tion — Suggestion and imitation — Cooperation — Insect societies 
are based mainly upon instincts 339 

CHAPTER XIX 

VERTEBRATE SOCIETIES 
Paleontological evidence of association among vertebrates — Fishes 

— Amphibians — Reptiles — Difference between cold- and warm- 
blooded vertebrates — Birds — The family — Mammals — Primates — 
Man 364 

CHAPTER XX 
THE FACTORS OF SOCIAL EVOLUTION 
The causes of association — The polyphyletism of animal societies 

— Utility for survival as a controlling factor in social evolution — The 
reasons for man's superior social evolution — Environmental forces 
for association — Instinctive forces for association — Is there a gre- 
garious instinct? — The sexual instinct — The reproductive instincts 

— The parental instincts — The utility of parental care — Conjugal 
relations — The family — Wider forms of association — The antago- 
nism between the family and the horde — The family as preparing 
the way for wider forms of association — Emotional forces for associ- 
ation — Intelligent forces for association — Imitation — Recognition 

— Communication — Language — The formation of categories — 
Meeting-places — Leadership — Theories of social evolution — The- 
ory of the instinctive origin of society : Petrucci, McDougall — The- 
ory of the emotional origin of society: Adam Smith, Sutherland — 
Theory of the intellectual origin of society : Giddings, Kropotkin, 
Tarde, Durkheim — The complexity of the factors in social evolution 390 

CHAPTER XXI 

CONCLUSION 
Summary of the preceding chapters — This book furnishes a basis for 
the study of the more complex human, mental, and social phenomena 422 



LIST OF FIGURES 

PIG. PAGB 

1. EUGLENA ViRIDIS 97 

2. Positive Chemotropism no 

3. Negative Chemotropism no 

4. Stereotropism, or Contact Irritability . . .113 

5. Amceba Proteus 119 

6. Paramecium 122 

7. Stentor Rceselii 125 

8. Diagram of a Typical Neurone 155 

9. Diagram of a Reflex Arc 159 

10. Diagram of the Central Nervous System facing 166 

11. Diagram of the Convex Surface of the Cerebral 

Hemisphere . , " . . . . facing 182 

12. Diagram of the Medial Surface of the Cerebral 

Hemisphere facing 182 



xvii 



THE SCIENCE OF HUMAN 
BEHAVIOR 

CHAPTER I 

THE STUDY OF BEHAVIOR 

Definition of behavior, i. — The science of behavior in relation to 
biology, psychology, and sociology, 2. — The genetic method of study, 
3. — Plan of this book, 4. 

The word '^behavior " has a variety of meanings. Some- 
times it is used in a very limited sense to refer to matters 
of deportment and etiquette. Sometimes it is used in 
a very broad sense to refer to the mode of acting of not 
only living beings, but also inanimate things such as an 
engine or a waterfall. Recently, however, there has been 
growing up a so-called "science of animal behavior" which 
has given to the word a very definite meaning. 

This science is being developed on the one hand by zo- 
ologists and on the other hand by comparative psycholo- 
gists. These scientists are studying those visible move- 
ments of the animal organism which constitute the external 
physiological processes. They are trying to explain these 
movements on the basis of anatomical structure and 
internal physiological processes stimulated by external 
forces. In other words, they are searching for a mechanical 
explanation of these movements. Their method of study 

B 1 



2 The Science of Human Behavior 

is therefore thoroughly objective rather than subjective 
in its character. This is very important in such a com- 
parative study of different species. Otherwise there would 
be great danger that the explanation of the movements 
of animals other than man would be too anthropomorphic. 
It is for this reason that the word "conduct" could not 
very well be applied to these movements, because this 
word has acquired an ethical connotation and is therefore 
highly anthropomorphic in its significance. The word 
''behavior" has no such connotation and is therefore the 
best one to apply to these movements. 

The science of behavior has already been claimed by 
several psychologists as constituting a part or the whole 
of psychology. But a little reflection will indicate that 
this cannot be so. The study of behavior must be to begin 
with and fundamentally biological, for, as we have seen, 
it involves the study of anatomical structure and physi- 
ological processes. In the second place, it is psychological, 
for mental forces are frequently involved in determining 
behavior. In the third place, it is sociological, for much 
behavior is influenced by the association of living beings. 
So that the science of behavior can be claimed by no one 
of these sciences to the exclusion of the others. It is a sort 
of hybrid product of these three sciences, and as such 
cannot be regarded as a primary science. But it is useful 
to call it a science as being a systematic study of these 
important phenomena. As a science it includes a small 
part of biology, but most if not all of psychology and soci- 
ology, for most if not all of mental and social phenomena 
can be reduced to terms of behavior. 

To begin the study of behavior from a biological point of 



The Study of Behavior 3 

view has, I believe, a very wholesome effect, for it necessi- 
tates the use of more or less exact methods of observation 
which are not always used in psychology and sociology. 
The use of these methods results in the disappearance of 
hazy and mystical explanations of human phenomena 
frequently proposed by writers in these two sciences. 
These explanations are replaced by more or less exact 
mechanical explanations. 

Furthermore, the genetic method of study involved is 
valuable for several reasons. It emphasizes the fact of 
evolution, which is as true of behavior as it is of all other 
phenomena. It makes use of the comparative method, 
by means of which much more can be learned about the 
behavior of a certain kind of animal than if the behavior 
of that species alone is studied. It resolves the complex 
forms of behavior into their simpler elements, thus making 
them much easier to understand. It thus makes many 
experiments unnecessary and at the same time shows what 
experiments should be made. 

In this book I have tried to lay the foimdations for the 
study of human behavior. This has involved bringing 
together, so far as possible within one book, the pertinent 
data from the three sciences of biology, psychology, and 
sociology. The book is, therefore, in a sense an introduc- 
tion both to psychology and to sociology. It has been 
written in the main from the objective point of view of 
the students of animal behavior. At the same time I do 
not think it possible to discuss human behavior and ignore 
the subjective side entirely. Consequently, at certain 
points, with the proper reserve and qualifications, I have 
made use of the subjective point of view. I have done so, 



4 The Science of Human Behavior 

however, without discussing the fundamental philosophical 
question as to the nature of knowledge. I am well aware 
that in one sense it is true that all knowledge is subjective. 
That is to say, all our knowledge comes to us through our 
senses in the form of sensations, and we cannot be abso- 
lutely certain that these sensations represent to us truly 
the nature of the world which is exterior to us. For 
scientific purposes, however, we need to practice what is 
sometimes called ^' naive reaHsm" and assume that things 
in the exterior world are actually as our senses represent 
them to be. 

In order to indicate the scope of this book I will outHne 
its contents briefly. The next chapter discusses the com- 
position of organic matter, showing how its mobile and 
unstable nature makes possible the plasticity of living 
organisms, thus furnishing a basis for the evolution of 
behavior. The third and fourth chapters furnish a brief 
survey of organic evolution, showing how the structural 
forms and physiological processes which condition be- 
havior have evolved and what forces are at work in the 
animal world, such as heredity, variation, selection, etc. 
The next two chapters deal with the behavior of animals 
without a nervous system, the fifth chapter describing the 
irritability of organic matter and the external forces which 
act upon organisms, and the sixth chapter deaHng with 
tropisms or the direct reactions of these lower animals to 
these external forces. The seventh chapter describes the 
factors at work in the evolution of behavior, with illustra- 
tions from the behavior of the lower animals. 

The next three chapters deal with the nervous system, 
describing briefly the evolution of the nervous system, the 



The Study of Behavior 5 

reflex action, which is the principal type of behavior deter- 
mined by the nervous system, the functions of the nervous 
system, and the localization of these functions. The fol- 
lowing three chapters deal with instinct as one of the 
principal types of behavior. In the eleventh chapter in- 
stinct is described as an inherited combination of reflexes 
integrated by the central nervous system. In this and the 
next chapter are described the structural basis of instinct, 
variations in instincts, and the different kinds of instincts. 
The thirteenth chapter discusses the principal human in- 
stincts and the general innate tendencies, such as imitation, 
play, habit, etc. 

The fourteenth chapter treats of intelligent behavior as 
behavior varied in response to experience. This involves 
a discussion of the different theories as to the nature of 
intelligence and a review of the experiments which have 
been made as to the range of intelligence in the animal 
world. In the fifteenth chapter are discussed the theories 
as to the nature of consciousness and sensations, feelings, 
emotions, and ideas as contents of consciousness. In the 
sixteenth chapter are discussed self-consciousness, the rela- 
tion between intelligence and consciousness, and the nature 
of mind. An attempt is made to show the inherent nature 
of mental or psychic phenomena and to point out the sig- 
nificance of these phenomena for behavior. Throughout 
these three chapters on intelligent and conscious phenomena 
the causes for the superior mental development of man are 
pointed out whenever they can be discerned. 

The next four chapters deal with social phenomena. 
In the seventeenth chapter are discussed the nature of 
association and the external and internal forces which 



6 The Science of Human Behavior 

caused the beginnings of social evolution. The eighteenth 
chapter deals with insect societies and in particular the 
ants, illustrating polymorphism or more particularly the 
physiological division of labor which results from it as a 
cause of association. The nineteenth chapter describes 
the kinds of societies existing among the different classes 
of the vertebrates with special reference to the mammalian 
and primate societies to which human society is most 
closely related. In the twentieth chapter are discussed 
the environmental, instinctive, emotional, and intelligent 
causes of association and the theories which have been 
proposed as to the origin of society. The concluding chap- 
ter summarizes very briefly the ground covered in this 
book. 

In these chapters, then, are described the different types 
of behavior, and in all of them, and especially in those on 
social behavior, the attempt is made to show how they are 
combined in the complex behavior of the higher animals 
and especially of man. But to analyze this combination 
is a very difficult thing to do, and only the bare beginning 
of such an analysis is made in this book. As the study of 
behavior is continued, this analysis of the combination of 
the different types of behavior can be carried further, but 
it can probably never be carried to the same degree of 
precision as the analysis of certain other kinds of natural 
phenomena, such as physical and chemical phenomena. 



CHAPTER II 

THE PHYSICO-CHEMICAL BASIS OF BEHAVIOR 

Physical and chemical characteristics of matter, 7. — Reasons for 
the mobile and plastic character of organic matter, 12. — The origin 
of the organism, 16. — The cell, 16. — The constituents of organic 
matter, 17. 

All forms of matter respond to external forces in the 
sense that changes take place in them when these forces 
act upon them. But this is peculiarly true of organic 
matter in the sense that in response to external forces 
living organisms will go through movements which are 
sometimes very complex in their character. As we have 
seen in the last chapter, these movements constitute be- 
havior. In order to understand the mobile and plastic 
character of organic matter, which makes behavior possible, 
it is advisable to consider some of the characteristics of 
matter in general. 

Characteristics of Matter 

The two sciences that deal with matter in general are 
physics and chemistry. Physics deals with matter in its 
simplest form. According to the physical sciences the 
fundamental entities to which all things can be reduced 
are matter and energy. To these is sometimes added 
ether, but of the existence of ether as a distinct and sepa- 
rate entity we have as yet no proof, and it may be no more 

7 



8 The Science of Human Behavior 

than a rarefied form of matter. Outside of these entities 
all else is more complex in character and can be reduced 
to these entities. As to whether these entities are irre- 
ducible we do not yet know, but it is possible that mat- 
ter can be reduced to energy. It is also possible that 
energy can be reduced to something more simple, in 
which case neither matter nor energy is a fundamental 
entity. 

Chemistry deals with matter in its complex forms. 
Matter usually manifests itself to the senses in the form of 
compounds, and chemistry is occupied with reducing these 
compounds to their elementary parts. About eighty of 
these elements have been distinguished, and so far as we 
know every compound in the universe is made up of a 
combination of some of these elements. The unit of each 
of these elements is called its atom. The smallest amount 
of an element or of a compound composed of two or 
more elements which can exist in a free state is called a 
molecule. 

For a long time it was thought that the atom of each 
element was irreducible and that these elementary atoms 
were ultimate forms of matter. This belief was effectually 
shaken by the discovery of the periodic law. This law 
was discovered as a result of a comparison of the weights 
of these elementary atoms. It was found that when these 
atomic weights are arranged in tabular form, as, for ex- 
ample, on the basis of hydrogen as one, or of oxygen as 
sixteen, many of them are even numbers or almost even 
numbers. The first hypothetical explanation of this was 
that each of the atoms is made up of a combination of 
atoms of hydrogen, which is the lightest element. Not all 



The Physico-Chemical Basis of Behavior 9 

of the atomic weights, however, are even numbers when 
the hydrogen atom is reckoned as one, so that hydrogen 
could not be regarded as the ultimate form of matter. 
But it was discovered that the elements when arranged 
in the order of their atomic weights naturally fall into 
groups of elements whose behavior is similar. These simi- 
larities and relationships seem to indicate that these 
elementary atoms could not be irreducible units, each 
of them absolutely distinct from and unrelated to all 
the others. On the contrary, it seemed very evident 
that there must be a unit or units smaller than the 
smallest of the elementary atoms out of which these 
atoms are formed, and that the similarities of these atoms 
must be explained by the similarity of their component 
parts. 

The fact of subatomicity or of the existence of particles 
smaller than atoms was thus made highly probable. But 
these particles are of necessity so small that for some time 
it was impossible to secure tangible evidence of their exist- 
ence, even with the most dehcate instruments. Such evi- 
dence was finally secured through a study of the conduc- 
tion of electricity by gases. It was found that electricity 
is conducted through gases by means of very small particles. 
These particles were named ions, those carrying negative 
electricity being called corpuscles or electrons. Little is 
known as yet with regard to the nature of positive electric- 
ity, but it is believed that the ions carrying particles of 
positive electricity are nearly as large as an atom. "The 
positive ion consists of an atom of the electrolyte with one 
of its corpuscles missing. In this way a unit of negative 
electricity is removed from it, that is, it is left with a posi- 



10 The Science of Human Behavior 

tive charge." ^ The negative ions or corpuscles or electrons 
are of greater interest to us, for they represent the smallest 
particles of matter of which we have tangible evidence. 

But the discovery that electricity is carried by these 
small particles of matter did not reveal the nature of elec- 
tricity itself, imless electricity is nothing more than these 
particles. That electricity is matter decomposed to an 
elementary form seems to be indicated by the fact that it 
possesses a fundamental property of matter, namely, 
inertia. This is asserted by an English physicist in the 
following words : ^'My first thesis is that an electric charge 
possesses the most fundamental and characteristic property 
of matter, viz., mass or inertia; so that if any one were 
to speak of a milligramme or an ounce or a ton of elec- 
tricity, though he would certainly be speaking incon- 
veniently, he might not necessarily be speaking errone- 
ously." 2 This may be stated just as well conversely, by 
saying that matter is electricity. 

Along with the development of the electrical theory of 
matter came the discovery of the new element radium. 
This element was found to possess the characteristic of 
radioactivity, or the power of emitting minute particles of 
matter. It was found also that these radiations were 
caused by a slow process of decomposition in the atom of 
radium, in the course of which the radium was becoming 
transformed into other elements. This discovery of the 
possibility of transformation among the elements raised 
the question whether matter in general is not unstable and 
in process of transformation. **Is matter in general under- 

» W. C. D. Whetham, The Recent Development of Physical Science, Philadelphia, 
1904, p. 190. ' Oliver Lodge, Modern Views on Matter, Oxford, 1903, p. 4. 



The Physico-Chemical Basis of Behavior 11 

going transformation? The raising of such a question 
would, until a few years ago, have been regarded as extraor- 
dinary, since the elements were regarded as stable and 
xmchanging. In the Hght of the recent investigations with 
the radioactive elements it is most pertinent. There is 
some evidence, as we shall see, that all the elements are 
radioactive to a very small extent. If this should be proved 
to be due to the elements themselves, to be a property in- 
herent in all matter, and not caused by the deposition of 
some form of radioactive matter, then, from what has been 
said above, we must regard matter in general as under- 
going change. This change is slow, very slow, but is 
progressing continuously; the more complex, imstable 
forms breaking down into simpler aggregates of electrons. 
If it should be shown that all matter is sHghtly radioactive, 
as seems not improbable, then we should be forced to the 
conclusion of the general instabihty of the chemical ele- 
ments." ^ 

The belief that matter is radioactive is based upon the 
electronic or corpuscular theory of matter, for transforma- 
tions in the atoms of the chemical elements would not be 
possible if the elements were simple and were not com- 
posed of still smaller imits. Furthermore, it is necessary 
to assume that there is a definite arrangement of the 
smaller units within each atom, and that when this arrange- 
ment is disturbed the atom is destroyed and that the 
atom of another element is formed. ''The electronic 
theory of matter supposes that an atom is composed of a 
swarm of electrons in rapid movement held in equiHbrimn 

1 Harry C. Jones, The Electrical Nature of Matter and Radioactivity, New York, 
1906, p. 161. 



12 The Science of Human Behavior 

by the internal forces of the atom. In the case of heavy 
atoms, like those of the radioelements, it is not necessary 
to suppose that each of these electrons has complete free- 
dom of movement. The character of the transformation 
of the atom suggests that it is built up in part of a number 
of secondary units, consisting of groups or aggregates of 
electrons in equilibrium, which are in rapid independent 
motion within the atom." ^ 

The corpuscular nature of the atom and the radio- 
activity of matter indicate that the elements are not im- 
mutable and that the atom is not the simplest form of 
matter. In all probability we shall never know the ulti- 
mate nature of matter, and this brief review of recent 
work in physics and chemistry emphasizes the mutable 
character of all the phenomena of which we can have any 
knowledge. It is therefore of utility in preparing the way 
for the study of that process of change in certain forms of 
matter which we call organic evolution. 

Organic Matter 

Let us now turn to the branch of chemistry which is of 
special significance for organic evolution, namely, organic 
chemistry. This branch of chemistry was named organic 
when it was beheved that there is an absolute distinction 
between organic and inorganic matter. "The word 
'organic' has now only a historic meaning, being derived 
from a time — the beginning of the last century — when 
it was thought that the substances which occur in organ- 
ized nature, in the animal and vegetable kingdoms, could 
only be formed under the influence of a special, obscure 

» E. Rutherford, Radioactive Transjormations, New York, 1906, p. 269. 



The Physico-Chemical Basis of Behavior 13 

force, called the vital force J ^ ^ This belief was destroyed 
by the discovery of the possibihty of forming organic com- 
pounds from inorganic materials by synthetic methods. 
This was first accompKshed in 1828 when the organic com- 
pound urea was synthesized from inorganic sources by 
Woehler. Since then many organic compounds have 
been synthesized, and it is no longer believed that any 
special vital force is necessary for the formation of organic 
matter. Organic chemistry is now frequently called the 
chemistry of carbon compoimds, because all organic com- 
pounds contain carbon. 

But while there is no absolute distinction between in- 
organic and organic matter, each has certain characteristics 
which differentiate it from the other, and we must study 
the peculiar characteristics of organic matter because it is 
these pecuKarities which have made biological, mental, and 
social evolution possible. These characteristics arise pri- 
marily out of certain pecuHarities of the principal elements 
in organic matter. The first of these is allotropism, or the 
capability of assuming different forms. For example, car- 
bon presents itself as diamond, graphite, and amorphous 
carbon, while oxygen appears under certain conditions as 
ozone. These allotropic forms of an element are appar- 
ently the result of different arrangements of the atoms 
within the molecules of the element. Analogous to allot- 
ropism in these elements is isomerism in many organic 
compounds. The isomeric compounds assume different 
forms, apparently as the result of different arrangements of 
the molecules of the elements within the molecules of the 

^ A. F. Holleman, A Textbook of Organic Chemistry, translated from the second 
Dutch edition by A. J. Walker, New York, 1903, p. 1. 



14 The Science of Human Behavior 

compound. These two peculiarities tend to make organic 
matter less stable and more subject to change than inor- 
ganic matter. Furthermore, they tend to make organic 
matter mobile. 

But there are other properties and forces which promote 
the instabiUty and mobihty of organic matter. *'0f the 
four chief elements which, in various combinations, make 
up living bodies, three are gaseous under all ordinary con- 
ditions and the fourth is a solid. Oxygen, hydrogen, and 
nitrogen are gases which for many years defied all attempts 
to liquefy them, and carbon is a solid except perhaps at 
the extremely high temperature of the electric arc. Only 
by intense pressure joined with extreme refrigerations have 
the three gases been reduced to the liquid form." ^ That 
three of the four principal organic elements are gaseous is 
of great significance with respect to the mobihty of organic 
matter, for the mobihty of the molecules of these elements 
promotes the mobihty of organic matter. The dissimi- 
larities of the organic elements are also of significance in 
this connection. *' These four elements of which organ- 
isms are almost wholly composed, exhibit certain extreme 
imhkenesses. While between two of them we have an 
imsurpassed contrast in chemical activity; between one 
of them and the other three, we have an unsurpassed con- 
trast in molecular mobility. While carbon, until lately 
supposed to be infusible and now volatilized only in the 
electric arc, shows us a degree of atomic cohesion greater 
than that of any other known element, hydrogen, oxygen, 
and nitrogen show the least atomic cohesion of all elements. 
And while oxygen displays, ahke in the range and intensi- 

' Herbert Spencer, The Principles of Biology, New York, 1900, Vol. I, p. 3. 



The Physico-Chemical Basis of Behavior 15 

ties of its affinities, a chemical energy exceeding that of any 
other substance (unless fluorine be considered an exception), 
nitrogen displays the greatest chemical inactivity.'' ^ As 
organic matter is made up of unlike elements, it is unstable, 
because these elements are easily separable by external 
forces. This instabihty causes mobihty and the capacity 
to dilBferentiate and integrate which make adaptation and 
biological evolution possible. 

On the other hand, the more complex forms of organic 
matter must have a certain amount of stability in order 
to make possible the growth of structures more or less 
permanent and rigid in character. "We may clearly see 
the necessity for that pecuHar composition which we find 
in organic matter. On the one hand, were it not for the 
extreme molecular mobility possessed by three out of the 
four of its chief elements ; and were it not for the conse- 
quently high molecular mobility of their simpler com- 
pounds ; there could not be this quick escape of the waste 
products of organic action; and there could not be that 
continuously active change of matter which vitality im- 
plies. On the other hand, were it not for the union of 
these extremely mobile elements into immensely complex 
compounds, having relatively vast molecules which are 
made comparatively immobile by their inertia, there could 
not result that mechanical fixity which prevents the com- 
ponents of Hving tissue from diffusing away along with 
the effete matter produced by decomposition." ^ 

We have been discussing the chemical properties of 
the organic elements which cause the instability and mo- 
biHty of organic matter. The question may naturally be 

» H. Spencer, op. cii.. Vol. I, p. S- ^ Ibid., Vol. I, p. 22. 



16 The Science of Human Behavior 

raised whether the recent discoveries in physics are not of 
significance in this connection. The discovery of radio- 
activity and of the electrical nature of matter revealing 
the fact of subatomicity has shown us that the chemical 
elements are much more complex than was formerly sup- 
posed. Whether, however, this is of pecuHar significance 
for the organic elements, we cannot yet know. If it should 
be found that the subatomic arrangement of the organic 
elements is more complex than that of the inorganic ele- 
ments, we might have a further explanation for the unstable 
and mobile character of organic matter. 

Origin of the Organism and the Cell 

Let us now consider the origin of the organism. The 
formation of the simplest organisms is probably comparable 
to the formation of crystals. In crystallization certain 
molecules which have been brought in close proximity 
with each other are drawn together by attractive forces 
which are inherent in them, thus forming crystals which 
are usually more or less symmetrical in shape. In similar 
fashion probably originated the primordial protoplasm out 
of which have evolved all organic forms. But the ele- 
ments which constitute organic matter possess chemical 
properties which make it more complex, more mobile, and 
more responsive and adaptive to its environment than 
most inorganic compounds, thus differentiating it from the 
ordinary crystal. 

The protoplasmic unit is the cell. The lowest organisms 
are unicellular, while the higher organisms are multicellular 
or made up of compounds of the unitary cell, 'the cell 
must have originated in the sea, for nowhere else could 



The Physico-Chemical Basis of Behavior 17 

the lowest forms of life have secured nutrition.^ On land 
an organism is not likely to come into direct contact with 
its food, and therefore needs sense organs to locate its food 
and means of locomotion to bring itself into contact with 
it. But in the sea the organism is constantly drifting into 
contact with food ingredients which are either dissolved 
in the water or in the form of solids. Then takes place the 
process of assimilation, metabolism, or nutrition, as it is 
variously called, when the food is absorbed into the organ- 
ism. Metabolism is primarily a phenomenon of chemical 
afl&nity. The chemical constituents of the organism have 
an affinity for the chemical constituents of the food, and 
therefore the organism absorbs the food. As the organism 
becomes more complex, metabolism becomes something 
more than a phenomenon of chemical affinity, because spe- 
cial organs within the organism are devoted to the assimi- 
lative process. 

That life originated in the sea is indicated by the fact 
that the constituent elements of sea water and air are 
approximately the same as the constituents of living matter. 
Sea water contains usually oxygen, nitrogen, carbon, hydro- 
gen, sodium, magnesium, potassium, calcium, chlorine, 
sulphur, and bromine. Air contains nitrogen, oxygen, and 
carbonic acid. The necessary constituents of hving matter 
which occur in every cell are oxygen, nitrogen, carbon, 
hydrogen, sodium, potassium, phosphorus, sulphur, cal- 
cium, magnesium, iron, and chlorine.^ In addition to 

1 Cf . Carl Snyder, The Physical Conditions at the Beginning of Life, in Science 
Progress, III, 12 (April, 1909), pp. 579-596. Snyder thinks that life did not originate 
in the sea, but that most of organic evolution has taken place in the sea. He does 
not state where else than in the sea life could have originated. 

* Max Verwom, General Physiology, London, 1899, pp. 99-102. 



18 The Science of Human Behavior 

these there occur in some cells silicon, fluorine, bromine, 
iodine, aluminum, and manganese, while sometimes there 
occur slight traces of certain metals such as copper. It 
will be noted that all of these necessary elements except 
iron and phosphorus are to be found usually in sea water 
and air, while a certain amount of iron and phosphorus 
must be dissolved in the water at the time living matter 
is generated. From the air, which is always in contact 
with the water and sometimes mingled with it, are derived 
some of the constituents of living matter. Organic evolu- 
tion must have begun when under favorable conditions ^ 
there was formed in the sea for the first time the primor- 
dial protoplasm out of which all organic forms have 
evolved. At first this protoplasm was, in all probabiHty, 
a formless, jellylike mass. Then out of it there evolved 
the organic cell, which is colloidal rather than crystalline in 
its character. 

We cannot trace this evolution fully, though a little of 
it is indicated to us by the cells in a plasmoidal state in 
which rigid cell walls have not as yet evolved. Whether 
protoplasm is still being generated in the sea or not, we can- 
not tell. If not, then all new Hving matter is reproduced 
from the old, but there is no reason to beheve that spon- 
taneous generation does not still continue. Experimenta- 
tion with protoplasm has always been very difiicult because 
of its extremely unstable character. A slight injury to the 
cell is almost certain to destroy its Ufe so that extended 

^ Cf. Snyder, op. cit.; A. C. Lane, The Early Surroundings of Life, in Science, 
Vol. XXVI, No. 6s7 (Aug. 2, 1907), pp. 129-143; Joseph McCabe, Evolution, 
New York, pp. 50-51. Snyder thinks these conditions were much the same as 
now. McCabc thinks they were very different, being much hotter and with a much 
heavier atmosphere. 



The Physico-Chemical Basis of Behavior 19 

experiments with it are almost impossible. But biologists 
may yet succeed in generating life by artificial means, and 
thus trace fully the course of organic evolution. 

This chapter has indicated briefly the characteristics of 
organic matter which furnish the physico-chemical basis 
for behavior. 



CHAPTER III 

THE ANATOMICAL AND PHYSIOLOGICAL BASIS OF BEHAVIOR 

Metabolism, 20. — Respiration, 20. — Circulation, 20. — Reproduc- 
tion, 21. — Sex, 22, — Theories of the origin of species, 23. — Orthogene- 
sis, 24. — NageH, 25. — Eimer, 27. — Differentiation of species through 
the action of external forces, 30. — Lamarck, 30. — Adaptation through 
the transmission of acquired characters, 30. — Darwin, 32. — Varia- 
tion, 32. — Selection, ^:^. — Criticisms of Darwinism, 35. — Weismann, 
38. — Inheritance through the germ cell, 38. — Germinal selection, 40. 
— Panmixia, 42. 

We must now study the anatomical and physiological 
characteristics of the organism in order to understand the 
structural forms and physiological processes which condi- 
tion behavior. This can best be done by means of a brief 
survey of organic evolution showing how these forms and 
processes have evolved and what forces have been and are 
at work in the animal world. 

Physiological Processes 

MetaboHsm is the fundamental process which goes on in 
living matter. There are certain other processes which 
characterize all Hving matter. Respiration is the process 
by which all effete matter and other matter not needed 
by the organism is oxidized and prepared for excretion. 
Circulation is the process by which water flows into the 
organism, carrying with it nutritive ingredients, and flows 
out of the organism, carrying with it the matter to be ex- 

20 



The Anatomical and Physiological Basis 21 

ere ted. All living matter is characterized by sensitiveness 
or irritability^ which makes it responsive to external in- 
fluences. I shall discuss this characteristic of living matter 
later in this book when deahng with the simplest reactions 
of organisms. As the organism evolves, it acquires a more 
and more definite form, and then a skeleton which fixes 
the character of the species and makes it more or less 
permanent. 

The assimilative capacity of the cell is Hmited. That 
is to say, when the cell attains a certain size its surface 
cannot adequately supply it with food because its bulk 
increases more rapidly than its surface. Furthermore, it 
becomes too bulky for the strength of the cell walls and 
breaks into two parts. This phenomenon marks the begin- 
ning of reproduction, for these two parts grow and become 
full-grown cells. I shall now discuss reproduction briefly 
from two points of view: on the one hand, as to the extent 
to which traits persist in reproduction ; on the other hand, 
as to the extent to which variation takes place in reproduc- 
tion. Both of these factors are of great importance in the 
determination of behavior. 

Reproduction 

The lowest type of reproduction has been mentioned 
above. When a unicellular organism becomes too bulky 
for the strength of its cell walls, and its volume is too great 
to be adequately supphed with food by its surface, so that 
its Hmit of growth has been attained, it separates into two 
parts, each of which becomes an organism. This is called 
reproduction by fission, and the division of the cell into 
two parts, which is characteristic of all cells, is called mitosis. 



22 The Science of Human Behavior 

The two new cells become more or less exact copies of the 
parent cell. Two other forms of reproduction which char- 
acterize certain unicellular and some of the lower multi- 
cellular species are reproduction by budding and sporula- 
tion. Both of these modes of reproduction are rare. In 
reproduction by budding, new cells grow out of the parent 
cell, thus forming a multicellular organism. Later the cells 
break off to become independent organisms, so that in re- 
production by budding we have a modified form of the 
division which takes place in reproduction by fission. In 
sporulation the parent cell breaks up into several parts, 
each of which becomes a new cell. 

In all forms of reproduction the reproductive power 
always resides apparently in the nucleus of the parent cell, 
a part of which goes into the formation of new cells. The 
characteristics of the parent are transmitted by means of 
the nucleus to its offspring. However, the cytoplasm of 
the cell which surrounds the nucleus probably has some 
influence upon inheritance, though how much is not yet 
known. Thus the nuclein or chemical compound called 
chromatin, out of which the nucleus is formed, seems to 
have the power of forcing the characteristics of the parent 
upon the offspring.^ 

So far I have been speaking of reproduction in species 
where the cells are all of the same kind. But this is true 
only of the lowest species. As we go up in the organic 
scale we find a specialization among the cells taking place. 
Certain cells called the germ cells become specialized for 
reproductive purposes alone, while the other cells or somatic 

* Cf . Jacques Loeb, in his essay Experimental Study of the Influence of Environment 
on Animals, in Darwin and Modern Science, edited by A. C. Seward, Cambridge, 1909, 
p. 247. 



The Anatomical and Physiological Basis 23 

cells no longer have any reproductive function, but per- 
form other functions in the individual organism. Further- 
more, there took place later on in organic evolution a special- 
ization among the germ cells themselves into ova or egg 
cells, and spermatozoa, or sperm cells. In all of the species 
in which the distinction of sex has appeared, reproduction 
cannot as a rule take place from a single germ cell as in 
the asexual species, but the ovum, or egg cell, has to be im- 
pregnated or fertilized by the spermatozoon, or sperm cell, 
before reproduction can take place. Furthermore, there 
appears among the individual members of these species 
the distinction of sex. The species is divided into females, 
who bear the egg cells, and males, who bear sperm cells, 
while in many other respects as well the two sexes differ 
greatly from each other. 

Origin of Species 

I have now reviewed briefly the origin and nature of 
life in general and also in individual organisms. The second 
great biological problem is that of the origin of species. 
This problem also is of great importance for the study of 
behavior, for each species is characterized by specific struc- 
tural forms and physiological processes which determine 
specific forms of behavior. It is hardly necessary to offer 
any proof as to the great diversity of species, since every 
individual has a personal knowledge of a large number of 
them. The first great division among organic species is 
that between animals and plants, while each of these 
classes may be divided into unicellular and multicellular 
groups. Animals and plants are therefore classified as pro- 
tozoa and protophyta, or unicellular animals and plants, and 



24 The Science of Human Behavior 

metazoa and metaphyta, or multicellular animals and plants. 
Among these species there is the greatest diversity of form, 
as indicated among animals by the differences between the 
minute insects and the huge mammalian forms, such as the 
elephant, and among the plants by the differences between 
the algae and the huge trees. The question as to how this 
great diversity of organic forms came into existence has 
always aroused a great deal of interest, and many theories 
have been propounded to explain it. It was at one time 
the popular belief that each species is a special creation of 
divine power, but more recently the attempt has been made 
to solve the problem of the origin of species in a scientific 
fashion on the basis of natural forces. I shall discuss these 
scientific theories under the following classification which, 
I believe, reveals best the peculiar characteristic of each 
group of theories. The first class explains the origin of 
species through orthogenesis ; the second class explains it in 
the main by the action of external forces upon the individual 
organism; the third class explains it by hetero genesis. 

Orthogenesis 

By orthogenesis it is meant that the organism has within 
it forces which carry it along a certain line of evolution 
independent of the external forces which play upon it. 
These internal forces arise in the first place out of the 
physical and chemical properties of the elements of which 
the organism is composed. It goes without saying that 
the first forces in organic evolution are the purely physical 
and chemical forces inherent in the elements which com- 
pose organic matter joined with the external molar forces 
which bring these elements together. Certainly no scien- 



The Anatomical and Physiological Basis 25 

tist to-day ought to believe in a supernatural vitalistic 
force as originating organic evolution. As has already 
been indicated, the forces which bring into being the 
organic cell may be similar to those which cause crystalli- 
zation in inorganic matter. The cell is similar to the 
crystal in its symmetry and definiteness of form, but is 
somewhat more complex. The forces which cause the 
crystal and the cell may in the main be called orthogenetic 
in the sense that they arise principally out of the inherent 
characteristics of the component parts of these organic 
forms. In the second place, as the organism grows more 
complex it develops forces peculiar to itself which force it 
along a more or less definite line of evolution. Thus ortho- 
genetic changes may take place in the cell as a result of the 
interaction of the parts of the cell, so that an evolution of 
the organism takes place independent of external forces. 
All orthogenetic theories attempt to explain organic evolu- 
tion and the origin of the different species by the workings 
of these internal forces. It goes without saying, however, 
that the orthogenetic theories postulate no supernatural or 
vitalistic force to account for organic evolution, but utilize 
only purely natural mechanical forces. 

Perhaps the most extreme example of an orthogenetic 
theory is that of NageH. He accounted for the earliest 
formations of organic matter by the purely physical and 
chemical laws which govern molecular matter, the process 
being similar to that of crystalKzation. Then as the or- 
ganism developed he believed that its evolution was di- 
rected in a definite course by what he unfortunately called 
a completing or perfecting principle (" Vervollkommungs- 
princip"). Some have thought that he meant by this a 



26 The Science of Human Behavior 

mystical vitalistic force, but the title of his principal work ^ 
indicates that he regarded it as a purely mechanical 
force. He believed that the existing species have evolved 
as a result of a phyletic force independent of any external 
forces, so that the existing species would have been the same 
had there been no selective forces, and all that selection has 
done has been to suppress certain species. There is, how- 
ever, no evidence of any such phyletic force independent 
of the forces inherent in the individual organism. As we 
shall see, the continuity of the germ cells is the only thing 
which is at all similar to a phyletic force. But this also is 
very different, because the evolution of the germ cells is 
not directed definitely towards the formation of a distinct 
species. 

Nageli was forced to take note of the adaptations which 
characterize all organic forms. He was, however, unwiUing 
to admit that these adaptations were permanent characters 
of a species. Adaptations might arise as a result of changes 
in environment and be transmitted by inheritance. But he 
contended that when the organism returned to its original 
environment it would soon lose its adaptive characters and 
would return to its original form which had been given to 
it by the phyletic force. This he illustrated in the case of 
certain plants which had originated at a low altitude and 
had then been transplanted to a high altitude. In the new 
environment in the course of several generations they ac- 
quired some new characters. But after being taken back 
to their original environment they lost their acquired char- 



^ Carl von Nageli, Mechanisch-Physiologische Thcorie der AbstammungsUhre, 
Munich and Leipsic, 1884; A Mechanico-Physiological Theory of Organic Evolution, 
Chicago, i8g8. 



The Anatomical and Physiological Basis 27 

acters and returned to their original form. It is evident 
that in this case Nageli is recognizing the influence of 
external forces and, furthermore, beHeved in the transmis- 
sion of acquired characters which, as we shall see, is very 
doubtful. 

This, however, shows that no theory of organic evolution 
can be purely orthogenetic, for however much the author 
of it may strive to account for organic evolution by a purely 
internal phyletic force, he is forced at some point to recog- 
nize the influence of external forces. 

This is especially true in the case of Eimer,^ who formu- 
lated an orthogenetic theory which is, next to that of Nageli, 
the best known. Eimer made extensive studies of the 
coloring of butterflies, and believed that he found in the 
progressive development of symmetrical color markings 
evidence of determinate evolution along orthogenetic 
lines. He thought he distinguished three main forces in 
organic evolution. The first he called genepistasis, or cessa- 
tion of development. He beHeved that certain individuals 
in a species cease to develop at a certain point in their life 
history, while other individuals develop further. Thus 
arise individual dift'erences which in course of time mark 
the distinction between two species. A different form of 
cessation of development he called heterepistasis. In this 
case certain individuals cease to develop in certain parts 
sooner than the rest of the species, and this gives rise to a 
new species. The second great force he called halmato- 
genesis, or saltatory variation. These sudden changes are, 

iTh. Eimer, Die Entstehung der Arten auf Grund von Vererbung erworbener 
Eigenschaften nach den Gesettzen organischen Wachsens, Jena, 1888; On Orthogenesis 
and the Impotence of Natural Selection in Species-Formation, Chicago, 1898. 



28 The Science of Human Behavior 

as he described them, similar to the mutations of De Vries 
which will be discussed later. The third great force was 
kyesamechania, or hindrance to fertilization. Such hin- 
drance might arise in several ways according to the nature 
of the species. If in a species fertilization comes about 
through direct contact of the external sexual organs, fer- 
tilization might be prevented by a disproportion in the size 
of these organs. In other cases fertilization might be pre- 
vented by the inabiHty of the sperm to penetrate the ovum 
either because the outer membrane of the ovum is too thick, 
or the sperm is too small and too weak to effect penetration. 
In still other cases the sperm might succeed in penetrating 
the ovum, but fertilization would not take place because of 
physico-chemical changes which had arisen either in the 
sperm or in the ovum which would cause sterility between 
the two. We shall see that Elmer's kyesamechania, or 
hindrance to fertilization, as a force in organic evolution 
was recognized by Romanes under the name of physio- 
logical selection. 

While these forces in organic evolution described by 
Eimer are in appearance internal, yet in trying to account 
for their origin Eimer gave great weight to external influ- 
ences. He discussed at great length the influence of tem- 
perature, nutrition, etc., in causing cessation of develop- 
ment, saltatory changes, and hindrance to fertilization. 
He has indeed been called a Neo-Lamarckian and illustrates 
very well how impossible it is for an orthogenesist to ignore 
external influences in organic evolution. His theory is 
orthogenetic mainly in the sense that he denied any in- 
fluence in evolution to indeterminate fluctuating variations 
and insisted that evolution is determinate. 



The Anatomical and Physiological Basis 29 

In every orthogenetic theory variations which have 
evolutionary value are called determinate in the sense that 
these variations are directed along one line towards the 
development of a distinct species form. In this respect 
orthogenetic theories vary, for example, from theories based 
upon selective forces at work upon variations fluctuating 
in all directions, as, for example, the Darwinian theory. 
It is, however, unfortunate that these variations are called 
determinate, for this word suggests a conscious directing 
power back of organic evolution, and, as has already been 
noted, none of the modern scientific orthogenesists postulate 
the existence of any such power. It would be well if the 
words ''determinate" and ''indeterminate" used in charac- 
terizing variation and evolution could be abolished from bio- 
logical literature, carrying with them the last vestige of a 
suggestion of a teleological force in organic evolution. 

All orthogenetic theories contain a measure of truth. As 
we have already seen, the generating of the primordial 
protoplasm, similar to crystalKzation, takes place in large 
part as a result of the molecular forces inherent in the ele- 
ments which constitute organic matter. The living cell, 
however, has much greater power than the crystal, for its 
nuclein acts as a ferment or enzyme for its own synthesis 
and synthesizes other nuclein of its own kind for new cells, 
thus determining the continuity of the species. As a rigid* 
anatomical structure develops, the line of evolution be- 
comes more or less narrowly limited and the organism is less 
amenable to external influences. Furthermore, symmetry 
and the correlation of parts have much to do with deter- 
mining the evolution of a species, as we shall see later on. 
But while organic evolution may be orthogenetic in all 



30 The Science of Human Behavior 

these respects, it would be a denial of the fundamental law 
of the conservation of energy to contend that external 
influences have nothing to do with organic evolution. Fur- 
thermore, the effect of external forces is to be seen in the 
extent to which all organic forms are adapted to their en- 
vironment, and orthogenesis can never explain these adap- 
tations, for it is inconceivable that all of them could be 
purely accidental and that there is no causal relation be- 
tween the environment and these adaptations. We shall 
therefore now turn to the theories which try to explain the 
origin of adaptations by giving great weight to external 
influences in organic evolution. 

Lamarck 

The first complete theory of organic evolution was that 
of the great French zoologist Lamarck.^ Lamarck was 
much impressed by the extent to which organic forms are 
adapted to their environment. He noted that adaptations 
acquired during the life of the individual usually result 
from use. For example, a muscle increases in size and in 
strength as the result of use. A portion of the skin which 
is frequently used in contact thickens. It occurred to him 
that the adaptations born in the individual result from the 
inheritance of characters acquired by his ancestors through 
use. Thus he explained the long neck of the giraffe by 
the habit of its short-necked ancestor of stretching its neck 
in order to eat the foHage on trees. He thought that the 
sHght increase in the length of the neck resulting from this 
habit was transmitted, and the cumulative result of many 
such transmissions is the present long neck of the giraffe. 

1 J. B. Lamarck, Philosophic zoologique, Paris, 1809. 



The Anatomical and Physiological Basis 31 

According to the same principle, the duck and goose have 
acquired their web feet as a result of the habit of their an- 
cestors of stretching the skin between the toes when strik- 
ing the surface of the water and birds have acquired their 
long toes as a result of the habit of grasping the limbs of 
trees. 

In similar fashion Lamarck explained the degeneration 
and disappearance of characters by disuse. He contended 
that if characters are acquired as the result of use, it is 
logical to assume that they will degenerate and disappear 
when they fall into disuse. Thus fish living in dark caves 
become bUnd because they no longer have any use for their 
eyes. 

Lamarck's explanation of the adaptation of a species to 
its environment through the transmission of characters 
acquired through use and of the degeneration and disap- 
pearance of these characters through disuse is a very plau- 
sible one and has therefore had a very wide currency. But 
Lamarck never offered a satisfactory explanation of how this 
transmission of acquired characters actually takes place. 
In order to furnish scientific proof of this theory, it would 
be necessary to describe the mechanism by which the 
characters acquired by the parent are transmitted to the 
offspring. Since no such mechanism was described by La- 
marck, and since no well-authenticated case of the transmis- 
sion of an acquired character has been observed, the La- 
marckian theory of organic evolution is now almost entirely 
discredited by scientists. As we shall see, the mechanism 
by which an organism inherits its traits is of such a nature 
that the traits acquired by its parents could hardly have 
any direct effect upon its inheritance. It is evident that 



32 The Science of Human Behavior 

theories of the origin of species through external forces must 
after all give great weight to internal forces, for the organ- 
ism must respond to these external forces and they have 
their effect upon the organism through the internal organic 
mechanism. But, on the other hand, we shall see that the 
characters acquired by individuals may indirectly have a 
great influence upon the evolution of the species. 

Darwin 

The next great theory of organic evolution based in the 
main upon the influence of external forces upon the or- 
ganism is that of Darwin. This theory coming as it did 
at an opportune moment has been the most famous of all 
theories of organic evolution. Darwin, like Lamarck, was 
much impressed with the extent to which organic forms are 
adapted to their environment. It was customary at that 
time to explain such adaptations teleologically as being the 
purposive acts of a divine power. For example, Paley in 
his famous treatise had likened the universe to a watch in 
which is revealed the design of its maker. But Darwin 
repudiated all such teleological explanations of adaptation 
and attempted to explain them on purely natural grounds. 
He had noted on the one hand that it is the tendency of 
every species to increase in numbers beyond the means of 
subsistence. The question therefore arose in his mind as 
to what determined which individuals were to survive and 
which were to perish. He had noted, on the other hand, 
that there are a great many congenital variations among the 
members of a species, which variations fluctuate around a 
central point. These variations are governed, as Quetelet 
later showed, by the law of probability, and the variations 



The Anatomical and Physiological Basis 33 

are usually no greater than to be included within a normal 
curve of frequency. 

It occurred to Darwin that the individuals who survive 
in the struggle for existence might be those characterized 
by variations which would be advantageous to them in 
this struggle for existence. If, therefore, the individuals 
with advantageous variations are constantly being selected 
for survival while the other individuals are perishing, and 
these variations are being transmitted, a species would 
gradually be characterized by the variations which have 
proved to be useful in its struggle for existence. The central 
thought, then, in the Darwinian theory, as indicated in the 
title of his great work,^ is that of selection which is con- 
stantly at work among fluctuating individual variations, 
preserving those which are advantageous and resulting in 
their transmission. Darwin and his followers have studied 
in great detail this force of selection and have distinguished 
many kinds of selection. 

Selection 

For example, Darwin believed that the so-called second- 
ary sexual characters, these being the characters which 
distinguish the sexes from each other, apart from the sexual 
organs which are the primary sexual characters, are the 
result of sexual selection. That is to say, the sexes in a 
species have been governed in their choice of mates by these 
characters. When a variation has appeared which has 
proved to be attractive to the opposite sex, it has been 
selected for survival by the advantage which that individual 

1 Charles Darwin, The Origin of Species by Means of Natural Selection or the Pres- 
ervation of Favoured Races in the Struggle for Life, London, 1859. 



34 The Science of Human Behavior 

had in mating. Darwin's critics, however, have contended 
that sexual selection cannot explain most of these secondary 
sexual characters, because it assumes aesthetic faculties much 
more highly developed than are to be found in most species. 

Romanes suggested what he called physiological selection,'^ 
or hindrance to fertilization, which, as we have seen, had 
already been described by Eimer under the name of kyesa- 
mechania. As a result of such restrictions upon the possi- 
bility of fertiUzation between certain individuals, certain 
types would be extinguished while others would survive, 
or two or more distinct types would survive which might 
in course of time become distinct species. 

Geographical selection or isolation as a force in organic evo- 
lution and in the formation of species has been discussed by 
Wagner, Romanes, Gulick, and others. If a portion of a spe- 
cies becomes isolated from the rest of the species by geograph- 
ical barriers or by any other means, a new species is Hkely 
to result from such isolation. If intercrossing is rendered 
entirely impossible between the two isolated groups, each 
group will tend to vary along its own lines, and in course 
of time there may be two species where formerly there was 
but one. Thomson has described this form of selection 
in the following words: ''This term is used to include 
all the means which restrict the range of intercrossing within 
a species : geographical barriers, such as arise when a pen- 
insula becomes an island ; temporal barriers, such as arise 
when the members of a species reach sexual maturity at 
different times of year ; hahitudinal barriers, when a species 
splits into two or more castes with different habits of life ; 
physiological barriers, such as arise by some variation in 

> G. J. Romanes, Journal of the Linnean Society, Vol. XIX, pp. 337-441. 



The Anatomical and Physiological Basis 35 

the reproductive organs ; and psychological barriers, which 
rest on profound antipathies.'' ^ 

Reproductive or genetic selection is a form of selection 
suggested by Karl Pearson. If the highest fertility in a 
species becgmes correlated with certain characters, varia- 
tions in those characters will have the advantage, because 
they will be reproduced most frequently. Thus those 
variations are most likely to persist and become charac- 
teristic of the species. 

It is impossible in this brief review to discuss at greater 
length the subject of selection, to which a great deal of 
study has been given. I shall now take up the principal 
criticisms of the Darwinian theory, which are of great im- 
portance because they have stimulated much of the recent 
work in biology. 

Criticisms of Darwinism 

The first main criticism of Darwinism as a synthetic 
theory of organic evolution is that it gives no adequate 
explanation of the origin of individual variations. It is 
true that Darwin offered his theory of pangenesis ^ as a 
tentative explanation of the origin of variations. But 
Darwin himself was very uncertain as to the soundness of 
this theory, and since his time no evidence has been found 
in support of it. According to this theory the germ cells are 
formed by small particles, which Darwin called gemmules, 
which are thrown off by the somatic cells in all parts of 
the organism. Now if any new characters have been ac- 
quired by the somatic cells, they will be reflected in changes 

1 J. A. Thomson, Darwinism and Human Life, New York, 1909, pp. 210-11. 

* Darwin, The Variation of Animals and Plants under Domestication, London, 1868. 



36 The Science of Human Behavior 

in these gemmules which compose the germ cells. Thus 
acquired characters will cause changes in the germ cells and 
variations in the offspring. So that Darwin's pangenetic 
theory is Lamarckian in that it recognizes the influence of 
acquired characters in heredity. He went further than 
Lamarck, however, in suggesting definitely by what mech- 
anism this transmission of acquired characters takes place. 
It is curious that Darwin, who had repudiated Lamarckism 
elsewhere, should have recognized it in his theory of pan- 
genesis. Beyond presenting this theory, Darwin had no 
explanation to offer as to the origin of variations. 

The next great criticism of the Darwinian theory was 
that variations are not at their origin usually of sufficient 
size to be advantageous or disadvantageous in the struggle 
for existence. The fortuitous, fluctuating variations which, 
according to the Darwinian theory, furnish the material 
for natural selection are usually so insignificant that they 
cannot have a hfe-or-death value in the struggle for ex- 
istence of the individuals characterized by them. For 
example, the polar bear whose white fur is undoubtedly 
advantageous to it has in all probability descended from 
the brown bear. But if it has acquired its white coat 
through the selection of favorable fluctuating variations, it 
is difficult to see how the first white hairs or small patches 
of white which appeared in the fur of certain of the brown 
bears could have had suflGicient selective value to give these 
individuals the advantage over their fellows. It is evident 
that a variation, even though it is in a favorable direction, 
has no advantage over other variations unless it has im- 
mediate selective value, for otherwise it will be swamped 
by interbreeding. A variation must therefore be of sufli- 



The Anatomical and Physiological Basis 37 

dent size to be of immediate selective value if it is to be 
perpetuated. But the critics of Darwinism have contended 
that most of the fluctuating variations are not of sufficient 
size to have selective value, and therefore selection could 
not have been the main force in the origin of species and 
in organic evolution. 

Another criticism which has been made of the Darwinian 
theory is that there has not been enough geological time for 
organic evolution according to Darwinian methods. It is 
evident that the selection of sHght variations is a slow pro- 
cess, and that it would take a vast number of such varia- 
tions to build up the complex organic forms now in existence. 
It was estimated by Kelvin, Tait, and others by means of 
deductions made from the central heat of the earth, from 
the rate of deposition of the calcareous deposits, from the 
increase in the amount of salt in the sea, and from various 
other sources, that the surface of the earth has been inhabit- 
able for a period under one hundred million years. Some 
of the Darwinian evolutionists have estimated that it must 
have taken thousands of millions of years for organic evolu- 
tion by the selection of sHght variations. If, therefore, the 
estimates of these physicists are correct, there has not been 
sufficient time for Darwinian evolution. But the recent 
discovery of radium has revealed sources of heat in the sun 
which were not conceived of before. This indicates that 
the Ufe of the earth may have been very much longer than 
was estimated by Kelvin and Tait, and that there may 
have been enough time for Darwinian evolution. 

It is needless to emphasize here the vast influence which 
the Darwinian theory has had. As has already been noted, 
Darwin was determined to account for the origin of species 



38 The Science of Human Behavior 

and organic evolution on natural grounds, and with pains- 
taking care he accumulated a vast amount of data to sup- 
port his brilliant generalizations. His theory came with 
convincing power to his own generation and proved once 
for all the fact of organic evolution, while it also threw a 
great deal of Hght upon the manner in which this evolution 
must have taken place. But, as we have seen, serious 
criticisms have been made of the Darwinian theory, and we 
must discuss the theories which are trying to supplant the 
Darwinian theory. Before doing so I wish to discuss the 
theories of the great Neo-Darwinian biologist, Weismann,^ 
who, though he has varied in several important respects 
from Darwin, has tried to answer the criticisms of Darwin 
and to prove the validity of the central Darwinian doctrine. 

Weismann 

The first great accompHshment of Weismann was that he 
completely refuted the Lamarckian theory. In this respect 
he varied from Darwin, since, as we have seen, Darwin 
was not entirely free from Lamarckism. By means of a 
painstaking analysis of many of the supposed cases of La- 
marckian inheritance, Weismann showed that the heredi- 
tary transmission of characters acquired through use and 
disuse is not possible. On the contrary, he showed that 
inheritance must be through the germ cells, upon which 
acquired characters can have no direct effect. He there- 
fore devoted much attention to the study of the constitution 
of the germ cells. He described the constitution of the 
germ cell as follows. The lowest chemical unit in the germ 

* A. Weismann, The Germ Plasm, London, 1893 ; On Germinal Selection as a 
Source of Definite Variation, Chicago, 1896. 



The Anatomical and Physiological Basis 39 

cell as elsewhere is the molecule. The lowest biological 
unit is, however, more complex and is composed of a num- 
ber of molecules. This biological unit Weismann called 
biophor. The biophor is a true form of Hving matter in 
that it absorbs nutriment during its Hfe. These biophors 
are organized into determinants, each of which represents a 
special kind of somatic cell. The determinants are in turn 
organized into ids, each of which represents a distinct part 
of the organism. Assuming as he did that inheritance is 
entirely through the germ cells, it was incumbent upon 
Weismann to describe the mechanism by which the germ cell 
determines the character of the fully developed organism. 
He was not the first who discussed the structure of the germ 
cell, for various other biologists have set forth hypotheses 
as to this question. We find several of them postulating 
ultimate biological units like Weismann's biophors. Thus 
we have Darwin with his gemmules, Spencer with his phys- 
iological units, NageH with his micellae, Galton with his 
stirps, De Vries with his pangenes, Haeckel with his plasti- 
dules, etc. All these so-called micromeric theories- assume 
that each character in the fully developed organism can be 
traced back to a unit in the germ cell. There have been 
other theories as to the constitution of the germ cell and the 
mechanism of inheritance, such as the biogen theory of 
Verworn, the physical machine theory of Delage, the 
chemism theory of Le Dantec, but I have no space to 
discuss these theories here. It has so far been impossible 
to furnish any positive proof of any of these theories be- 
cause of the microscopic and unstable nature of the germ 
cell. It is, however, necessary for each writer on the sub- 
ject to adopt some sort of an hypothesis as to the nature 



40 The Science of Human Behavior 

of the germ cell, however impossible it may be to prove or 
disprove this hypothesis. 

Having assumed an hypothesis as to the nature of the 
germ cell, Weismann now turned his attention to answering 
the critics of Darwinism. He was forced to admit that 
many favorable variations are not at first of suflSicieni: size 
to possess a life-or-death significance in the struggle for 
existence. In order, therefore, to explain how slight favor- 
able variations are preserved, he set forth his theory of 
germinal selection. This theory extends the idea of selec- 
tion to the germ cell and assumes a selective process among 
the parts of the cell as well as among complete organisms. 
We have already noted that Weismann believed that the 
units within a cell absorb nutriment as well as the cell as 
a whole. There may therefore arise among these units a 
struggle for nutriment. If one of these units happens to be 
a Httle stronger than the others, it will secure a larger share 
of the nutriment and will therefore grow to a larger size. 
Its increase in size will give it still further advantage in the 
struggle for nutriment, and will result in a further increase 
in size. This advantage secured by one determinant over 
others would be perpetuated from generation to generation 
of germ cells, and thus variation in a definite direction would 
come about. Such definite variations would in the case of 
some determinants be in the direction of degeneration and 
decrease in size where the determinant is at a disadvantage 
in the struggle for nutriment. These variations in a definite 
direction in determinants would be manifested in definitely 
directed variations in the fully developed organism. But 
these variations might for a long time not be of sufficient 
size to have selective value. As soon, however, as the 



The Anatomical and Physiological Basis 41 

variation had become of sufficient size to have life-or- 
death significance, external forces would immediately exert 
a selective power over them, preserving and perpetuating 
the individuals manifesting favorable variations and sup- 
pressing those with unfavorable variations. 

Weismann believed that by means of his theory of ger- 
minal selection he was able to show how variations are 
furnished as material for natural selection. But while he 
has extended the idea of a struggle and of selection to the 
germ cell, it is evident that this struggle and selection are 
very different from the Darwinian struggle for existence and 
natural selection. The Weismannian theory differs very 
greatly from the Darwinian in that the materials for selec- 
tion are no longer slight fluctuating variations, but variations 
of considerable size directed in a definite line of develop- 
ment. Thus the theory of germinal selection is more nearly 
a causo-mechanical explanation of orthogenetic variation, 
that is to say, variation directed along a definite line by 
internal forces, than it is a theory of variations caused by 
external forces. The theory of germinal selection may be 
true, but it furnishes no assistance to the Darwinian theory 
of natural selection. 

Another criticism of the Darwinian theory has been that 
it fails to account for the degeneration of useless parts. If 
a useless part is harmful to the organism and hinders it in 
the struggle for existence, it will be ehminated by natural 
selection. But if the useless part is harmless and does not 
hinder the individual in the struggle for existence, there 
seems to be no reason why it should not persist in its full 
vigor as much as the useful parts. Weismann endeavored to 
explain the degeneration of useless parts by means of his the- 



42 The Science of Human Behavior 

ory of panmixia. As we have seen, variations come about 
as a result of the success or failure of the determinants to 
secure nutriment. When a variation has become of suffi- 
cient size to be of life-or death significance, if it is advan- 
tageous it will be preserved and encouraged by natural 
selection, if it is disadvantageous it will be suppressed in 
a similar fashion. A variation may, however, be neither 
advantageous nor disadvantageous, or after having been ad- 
vantageous, it may have become useless. In this case it 
will no longer have the force of natural selection in its sup- 
port. It will therefore persist only so long as its determi- 
nant is successful in securing nutriment. When its deter- 
minant happens to lose in this struggle, a definitely di- 
rected downward variation will commence which will not be 
checked by natural selection, and thus the part will degener- 
ate and may in course of time disappear entirely. Thus, 
according to Weismann's theory of panmixia, in the mixing 
of parts which takes place at reproduction the determinants 
which represent the parts which are advantageous to the 
organism, and are therefore being supported by natural 
selection, will have the advantage in the struggle for nutri- 
ment within the germ cell, while the determinants which 
represent useless parts will lack the support of natural 
selection and are certain in course of time to lose ground 
in the struggle for nutriment and to degenerate. The the- 
ory of panmixia is, however, as hypothetical as the theory 
of germinal selection and the nature of the germ cell as de- 
scribed by Weismann, so that it is impossible to say how true 
an explanation it is of the degeneration of useless parts. 
Certain it is that many such useless parts are to be found in 
the vestigial and rudimentary organs which exist in all 



The Anatomical and Physiological Basis 43 

organic forms, and for which an explanation must be given 
in any complete theory of organic evolution. 

Weismann devoted a good deal of attention to the expla- 
nation of the origin of variations. We have already seen in 
the theory of germinal selection how variations may come 
about as the result of changes in the nutriment of the de- 
terminants. Weismann believed furthermore that amphi- 
mixis, or reproduction by two parents, is of great value in 
stimulating variabiHty. In amphimixis two hues of de- 
scent are crossed, and in the mixing of determinants 
which takes place there is much greater possibility of 
new combinations of characters. Some attempt has been 
made to determine whether there is more variability in 
amphimixis than in self-fertilization or parthenogenesis. 
Nothing conclusive has been learned, though there is 
some indication that there are no more slight fluctuating 
variations in amphimixis than in other forms of repro- 
duction. But this does not mean necessarily that am- 
phimixis does not cause more of the large non-fluctuating 
variations. 

Weismann has insisted that he has proved that variation 
is guided by utihty, and that the degree of adaptiveness of a 
part evokes the direction of variation of that part. He has 
furthermore insisted that he has proved that there is no 
conscious directing power in adaptations, however purpo- 
sive they may seem. We have seen that he may not be 
correct in thinking that all variations are guided by utility, 
inasmuch as some of them may be orthogenetic in their 
origin and therefore independent of considerations of 
utility. But there can be little doubt that Weismann, next 
to Darwin, has done more than any one else to show that 



44 The Science of Human Behavior 

organic evolution has not in the slightest degree been teleo- 
logical, but has been the result of purely natural forces. 
Furthermore, Weismann has stimulated greatly the study 
of the mternal forces in organic evolution by insisting that 
the germ cell is the sole agent of heredity. 



CHAPTER IV 

THE ANATOMICAL AND PHYSIOLOGICAL BASIS OF BEHAVIOR 

(Continued) 

Heterogenesis, 45. — Discontinuous variations, 46. — Bateson, 46. 

— Substantive and meristic variations, 46. — Symmetry, 47. — De 
Vries, 51. — The mutation theory, 51. — Micromeric theories of the 
germ cell, 53. — Unit characters, 55- — Mendel, 55. — The Mendelian 
law of inheritance, 55. — Dominant and recessive characters, 55. 
— The segregation of allelomorphic characters, 56. — Homozygotes 
and heterozygotes, 56. — The Mendelian explanation of particidate, 
exclusive, and blended inheritance, 57. — Reversion or atavism, 59. 

— Galton's laws of ancestral inheritance and of filial regression, 60. 

— Mendelian criticism of Galton's laws, 60. — Statistical and physio- 
logical laws of inheritance, 60. — The exaggerated claims for Men- 
dehsm, 63. — Johannsen's theory of pure Unes, 64. — Sex determina- 
tion, 65. — Sex as a unit character, 66. — ^The biological basis for 
psychology, anthropology, and sociology, 68. 

We have now discussed orthogenesis as represented in the 
theories of Nageli and Eimer and theories of organic evolu- 
tion based in the main upon the action of external forces as 
represented in Lamarck and Darwin, while in Weismann we 
find an example of a theory of organic evolution which com- 
bines the internal with the external forces. Weismann will 
therefore serve well as an introduction to heterogenetic 
theories of organic evolution. 

Heterogenesis 

By heterogenesis it is meant that organic evolution and 
the origin of species have resulted from occasional, sudden, 

45 



46 The Science of Human Behavior 

and fixed variations which may be large or small, and which 
appear in offspring and form the starting point for new 
types and species. Inasmuch as the heterogenesists ac- 
count for these sudden variations or mutations, as they are 
frequently called, by the interaction of internal ortho- 
genetic forces and external environmental forces, hctero- 
genetic theories form a type which is a sort of combination 
of the two types of theories which I have been discussing. 
Heterogenetic variations are usually called discontinuous 
in the sense that they do not come gradually as the result 
of sHght changes, but suddenly and all at once. In this 
respect they are contrasted with the continuous Darwinian 
variations, which appear as the result of the selection 
of sHght fluctuating variations. Discontinuous variations 
are not governed by the law of probabiHty Hke the fluctuat- 
ing variations and do not fall within a normal curve of 
frequency. Heterogenesis as a theory of species forming 
has been advocated by various biologists since the time of 
Darwin, such as von Kolliker, Galton, Bateson, Emery, 
Korschinsky, de Vries, etc. Some of these biologists have 
been anti-Darwinian ; others have agreed with the Darwin- 
ian theory in the main, but have varied from it in beHeving 
that discontinuous variations have had something to do 
with the formation of species. I wish to speak in particu- 
lar of the theories of Bateson and of de Vries. 

Bateson 

Bateson ^ classifies variations as falling under two main 
types, namely, substantive variations and meristic varia- 
tions. By a substantive variation he means any change 

1 W. Bateson, Materials for the Study of Variation, London, 1894. 



The Anatomical and Physiological Basis 47 

in the internal composition or structure of any part of the 
organism. By a meristic variation he means any change in 
the arrangement or repetition of the parts of the organism. 
He has enumerated and described a large number of cases 
of meristic variation. In introducing the description of 
these variations he has discussed at some length the sub- 
ject of symmetry in organic forms. 

Symmetry is an almost universal phenomenon in the 
organic world. Three main types of symmetry may be dis- 
tinguished, — linear, bilateral, and radial symmetry. In 
linear symmetry parts are repeated in consecutive order, as, 
for example, in the case of the rings of a worm or snake or 
of the vertebrae in a vertebrate. In bilateral symmetry a 
part is repeated once in a corresponding position, as in the 
case of the arms and the legs of a vertebrate. In radial 
symmetry parts are repeated, branching out from a central 
point, as in the tentacles of a starfish or the petals of a 
flower. Some have reasoned in accordance with the Dar- 
winian theory that symmetrical forms are adaptations re- 
sulting from the workings of natural selection. It is true 
that symmetrical parts do frequently adapt an organ- 
ism to its environment. For example, freely moving 
animal forms are usually characterized by linear and bi- 
lateral symmetry, though a few freely moving animals are 
characterized by radial symmetry, as, for example, the sea 
urchin. Immobile plant forms usually display radial sym- 
metry, though linear S)nnmetry also is frequently found, 
as in the stalk of a plant, and bilateral symmetry less fre- 
quently, as in some forms of flowers. Immobile animal 
forms also are usually characterized by radial symmetry, 
as, for example, the sea anemone. But the fact that symme- 



48 The Science of Human Behavior 

try is frequently advantageous to an organic form does 
not prove necessarily that it is an adaptation. For ex- 
ample, it has been pointed out that the symmetry is fre- 
quently more perfect than is necessary for adaptation, so 
that there must have been some force at work apart from 
adaptation in causing this symmetry. Furthermore, sym- 
metry is sometimes disadvantageous to an organic form. 
These facts indicate that symmetry is probably caused in 
the main by orthogenetic forces and that, though natural 
selection may have suppressed many symmetrical forms 
which have proved to be disadvantageous and has preserved 
many other symmetrical forms which have proved to be 
advantageous, it has had nothing to do with causing this 
symmetry. 

I have already called attention to the fact that crystals 
are symmetrical like organic forms. It is quite possible 
that such symmetry as exists in the primordial protoplasm 
has been caused in a fashion similar to the symmetry of 
crystals ; namely, by the forces inherent in the molecules of 
the elements which composed it. But this would not be a 
sufficient explanation for the symmetry which characterizes 
more complex organic forms. The symmetry of these 
complex forms must in all probability be traced back to 
the mitosis or division of the cell. All organic growth takes 
place as the result of such mitosis. A cell usually divides 
into equal parts, and the nuclein which is divided between 
the two new parts carries the same characters, so that it is 
not surprising that there should be the repetition of parts 
which, as we have seen, characterizes symmetry. It 
has been observed in certain bilateral organisms that the 
first cell division marks the dividing line between the two 



The Anatomical and Physiological Basis 49 

corresponding sides of the organisms. The complete 
explanation of synmaetry would in all probability be much 
more complicated than has been indicated, but such a full 
explanation has not yet been furnished us by the biologists, 
and I have not the space to discuss it further here. What 
has been said is sufficient to indicate how symmetry may 
have resulted orthogenetically from the internal structure 
and forces of the organism. 

Bateson, who is opposed to Darwinism in certain im- 
portant respects, believes that symmetry is orthogenetic in 
its origin, though he offers no explanation for the develop- 
ment of symmetrical forms. Many of the discontinuous me- 
ristic variations which he has described are asymmetries or 
variations from the usual symmetrical forms. In another 
place he has suggested that heredity is a special case of the 
symmetrical division of the cell, while genetic variation is 
a consequence of asymmetrical division of the cell. As 
Bateson himself says, we know so Httle as yet with regard 
to mitosis that it is impossible to judge as to the validity 
of this hypothesis. Assuming, however, that these varia- 
tions do result from the asymmetrical divisions of the cell, 
the important question is as to whether these variations are 
perpetuated and become the permanent characters of a 
type. Such discontinuous variations have been observed 
for a very long time and have been called sports, mon- 
strosities, teratological forms, etc. They have usually 
been regarded as abnormahties which could not persist 
permanently, though sometimes reappearing through several 
generations. It has been contended that discontinuous 
variations are usually repetitions or misplacements of old 
parts, and not appearances of new structures ; that they are 



50 The Science of Human Behavior 

very rare, and are not usually inherited because they are 
swamped by intercrossing and so cannot account for the 
discontinuity of species. Bateson, however, beUeves that 
these discontinuous variations are inherited and may form 
the characters of a new type, though I suppose he would 
not deny that if these new characters were sufficiently 
disadvantageous to the organism they might be eliminated 
by natural selection. If his suggestion that discontinuous 
variations result from asymmetrical cell divisions is true, 
and that these discontinuous variations are inheritable, 
then he must believe that these variations are normally 
transmitted in symmetrical cell divisions. It would seem, 
then, as if the organism would in course of time lose all 
S3rmmetry if many of these variations took place. It may 
be, however, that not all of these asymmetrical cell divi- 
sions result in asymmetrical variations in the fully de- 
veloped organism, while the organisms which become most 
asymmetrical are eliminated by natural selection, because 
of their unfitness for their environment. 

At this point should be noted the part played by the 
correlation of parts as a cause of variation. Many of the 
parts of an organism are so related to each other that a 
change in one of them necessitates changes in the other. 
This may be because the parts are repetitions of each 
other as in symmetry, or because they grow out of and after 
each other. Thus a single variation at the origin of the 
individual organism may result in a more or less com- 
plicated series of changes in the fully developed organism. 



The Anatomical and Physiological Basis 51 

De Vries 

Let us now turn to de Vries/ who is perhaps tbxe most 
distinguished representative of the theory of the origin of 
species by discontinuous variations or mutations, as he 
usually calls them. De Vries has carried on many pains- 
taking experiments with plants in order to study these 
mutations. He has been most successful with the great 
evening primrose, or (Enothera Lamarckiana. This plant, 
which he beheves came from America, he found growing in 
a wild state near his home in Amsterdam apparently in 
a state of mutability. He experimented with this plant 
through several generations and secured seven varying 
forms which he believes are new mutations. These new 
forms bred true when self-fertilized, and de Vries beheves 
that they are elementary species. He has formulated the 
theory that an organism may pass through a state of mu- 
tabiHty when one or more of these mutations will appear. 
This idea had already been suggested by Galton under the 
name of organic instability, and had been aptly illustrated by 
him by means of a polyhedron, which is quite stable on one 
of its bases, but very unstable on another. Such instabiUty 
or mutability may be caused by a change in environment. 
Or it may result from the cumulative effect of forces in the 
environment which are causing sHght internal changes 
which suddenly manifest themselves in one or more external 
changes in the organism. Just how these environmental 
forces affect the germ cells in such a fashion as to cause 
these mutations has not been clearly shown by any of the 
mutationists. Their theory sounds a Kttle like Neo- 

1 H. de Vries, Die Mutaiionstheorie, Leipsic, 1901 ; Species and Varieties, their 
Origin by Mutation, Chicago, 1905. 



52 The Science of Human Behavior 

Lamarckism because of the emphasis which is laid upon the 
direct effect of the environment upon inheritance. But I 
believe they all repudiate Lamarckism, and they may yet 
succeed in showing how the environment can have this 
direct effect upon heredity. 

Unfortunately for de Vries, it has been said that the plant 
with which he experimented, the (Enothera Lamar ckiana, 
was a hybrid which had come from the Jardin des Plantes 
in Paris. If this is the case, these varying forms which 
he believed to be mutants may be ancestral forms reap- 
pearing in these descendants. Until this question is decided 
it will be impossible to estimate at its true value the work 
of de Vries. With regard to the mutation theory in general 
there have been as yet few if any well-authenticated cases 
of such mutations, for it is not always possible to tell whether 
or not these apparent mutations are the result of hybridi- 
zation. 

If the mutation theory could be proved, it would avoid several of 
the difficulties in the natural selection theory of the formation of 
species. Morgan has summed up the advantages of the mutation 
theory as follows : — 

"i. Since the mutations appear fully formed from the beginning, 
there is no difficulty in accounting for the incipient stages in the de- 
velopment of an organ, and since the organ may persist, even when it 
has no value to the race, it may become further developed by later 
mutations and may come to have finally an important relation to 
the life of the individual. 

"2. The new mutations may appear in large numbers, and of 
the different kinds those will persist that can get the foothold. On 
account of the large number of times that the same mutations appear, 
the danger of becoming swamped through crossing with the original 
form will be lessened in proportion to the number of new individuals 
that arise. 

"3. If the time of reaching maturity in the new form is different 



The Anatomical and Physiological Basis 53 

from that in the parent forms, then the new species will be kept from 
crossing with the parent form, and since this new character will be 
present from the beginning, the new form will have much better 
chances of surviving than if a difference in time of reaching maturity 
had to be gradually acquired. 

"4. The new species that appear may be in some cases already 
adapted to live, in a different environment from that occupied by 
the parent form ; and if so, it will be isolated from the beginning, which 
will be an advantage in avoiding the bad effects of intercrossing. 

"5. It is well known that the differences between related species 
consist largely in differences of unimportant organs, and this is in 
harmony with the mutation theory, but one of the real difficulties of 
the selection theory. 

"6. Useless or even slightly injurious characters may appear as 
mutations, and if they do not seriously affect the perpetuation of the 
race, they may persist." ^ 

MiCROMERic Theories 

It must be evident from what has gone before how im- 
portant it is to study the internal structure of the germ cell. 
If it be true, as Weismann and other great biologists have 
contended, that all inherited characters are transmitted 
through the germ cell and that all genetic variations arise 
in the germ cell, it is evident that we cannot hope to know 
much more about heredity and variation until we know 
more as to the nature of the germ cell. As has been noted, 
it is difficult to learn anything definite about the germ cell 
because of its miscroscopic size and unstable nature. And 
yet it is necessary for each writer on the subject to adopt 
some sort of an h3^o thesis as to the nature of the germ cell. 
Consequently there are numerous micromeric theories, 
as, for example, the gemmule theory of Darwin and the 
biophor theory of Weismann, in which it is assumed that 

* T. H. Morgan, Evolution and Adaptation, New York, 1903, pp. 298-299. 



54 The Science of Human Behavior 

each character in the organism can be traced back to a 
unit in the germ cell. By extirpating certain chromosomes 
in the germ cell and then noting how the organism which 
develops from it varies from the normal organism, it might 
be possible to determine whether specific characters are de- 
termined by specific units in the germ cell. This would 
furnish a test of micromeric theories. But it is doubtful 
if this experiment could be carried out successfully, partly on 
account of the minute size of the germ cell, but also because 
the shock of the operation would probably either kill the 
cell or at least derange its development very greatly. 

There has, however, been some criticism of these mi- 
cromeric theories. For example, Loeb has said that "mor- 
phological structures can only play a role through their 
physical and chemical properties, "^ thus insisting that the 
ultimate causes of the phenomena of heredity and variation 
are to be found not in any vital unit in the cell, but in the 
properties of the elements of which the cell is composed. 
Le Dantec^ has criticized much more drastically these 
micromeric theories. He says that the micromerists, while 
admitting that they cannot explain one of these units, have 
only complicated the problem by assuming a vast number 
of them. In the place of these micromeric theories he 
proposes his chemism theory. According to this theory a 
species is distinguished by the chemical composition of its 
germ cells. A chemism theory can take no primary ac- 
count of form, but as conditions of chemical identity will 
usually involve identity of form, the individuals composing 
a chemical species will possess a similar or identical form. 

^ J. Loeb, The Dynamics of Living Matter, New York, X906, p. 186. 
* F. Le Dantec, TraiU de biologie, Paris, 1906, 



The Anatomical and Physiological Basis 55 

There have been several other physico-chemical theories 

as to the nature of the mechanism by which the germ cell 

transmits characters, but I have not the space to discuss 

them here. 

Mendel 

The idea of unit characters, namely, the idea that the 
characters in an organism may be traced back to distinct 
units in the germ cell, is now very popular among biologists, 
probably in large part because of the rediscovery of the 
work of Mendel. The facts as to this rediscovery in the 
year 1900 are too well known to need repetition here. The 
discovery immediately aroused great interest, because it 
seemed to confirm conclusions arrived at by de Vries, 
Correns, Tschermak, and others. The significant thing 
about the work of Mendel was that he had devised an ex- 
perimental method of studying heredity and variation. 
After crossing certain species, varieties, or types he had 
traced the characters in which they differed through several 
generations in order to determine in what proportion and 
in what manner they reappeared. As a result of these 
experiments he formulated a law governing the trans- 
mission of unit characters in hybridization. Mendel had 
noted that in most if not all species, varieties, and types 
there are certain characters which when hybridization 
takes place do not blend with the corresponding characters 
in the other species, variety, or type. That is to say, in 
the hybrid either the one or the other of these alternative 
characters appears. Such characters have been called, I 
believe, by Bateson, allelomorphs. Mendel discovered that 
in some of these allelomorphic pairs of characters one of 
the characters is usually dominant and the other recessive. 



56 The Science of Human Behavior 

That is to say, the dominant character appears more fre- 
quently in the sum total of the offspring throughout any 
number of generations than the recessive character. 

Furthermore, he discovered what the proportion between 
the dominant and recessive characters in the offspring usually 
is. He found that in the first generation all the offspring 
bear the dominant character. But in the second generation 
three fourths of the offspring bear the dominant character 
while one fourth bear the recessive character. The descend- 
ants of the individuals bearing the recessive character display 
thereafter only the recessive character. Apparently, there- 
fore, the dominant character has been ehminated from the 
inheritance of this line of descent. Of the offspring bear- 
ing the dominant character in the second generation, one 
third give birth thereafter to individuals bearing only the 
dominant character. Apparently, therefore, the recessive 
character has been eliminated from the inheritance of this 
line of descent. The descendants of the other offspring 
in the second generation bearing the dominant character 
again break up into individuals bearing the dominant and 
recessive characters in a proportion of three to one, and the 
same process takes place of a segregation of lines of descent 
in which there is transmitted only one of the two characters. 

The fertilized germ cells in hybridization from which 
one of a pair of allelomorphic characters has been ehminated 
have been named homozygotes^ while the fertiUzed germ cells 
which bear both of the characters of an allelomorphic 
pair are called heterozygotes. The segregation of allelomor- 
phic characters in homozygotes has been called by Bateson 
the most significant part of the Mendehan law.^ Bateson 

i W. Bateson, Mendel's Principles of Heredity, Cambridge, 1909, chap. 15. 



The Anatomical and Physiological Basis 57 

believes that such segregation explains purity of type. 
That is to say, a pure-bred organism is one which is entirely 
homozygous. If this is true, the Mendelian law is of great 
value in showing what constitutes purity of type. 

It is beUeved by Mendelians that the Mendelian law 
explains some kinds of inheritance, while some of them seem 
to think that it explains all kinds of inheritance. For 
example, particulate or mosaic inheritance is explained by 
the Mendehans according to the Mendelian law. In such 
inheritance an offspring displays the characters of one parent 
in certain of its parts, while it displays the characters of the 
other parent in other parts, in such a fashion as to present 
a sort of mosaic pattern of the characters of the two parents. 
We have an example of this in the case of piebald coloring, 
where the offspring displays the color of one parent in 
certain parts of the body and of the other parent in other 
parts. The Mendehans beHeve that the offspring is thus 
displaying the unit characters of both parents. In the 
case of piebald coloring it is uncertain whether the appear- 
ance of the colors of both parents is due to imperfect domi- 
nance or is because the coloring of different parts of the body 
is represented by different unit characters. 

The Mendehans beHeve that exclusive inheritance also 
can be explained by the Mendehan law. In this form of 
inheritance the offspring resembles one parent exclusively. 
According to the Mendehans such inheritance takes place 
when one parent bears all the dominant characters ; that is 
to say, is thoroughly prepotent according to the older man- 
ner of expressing it. 

Some of the Mendehans seem to think that blended in- 
heritance also is explained by the Mendehan law. Such 



58 The Science of Human Behavior 

inheritance exists when the characters of the two parents 
are so mingled that neither character appears distinctly. 
Thus when a white is crossed with a negro there is derived 
a shade of black which is called mulatto. Karl Pearson ^ 
states that he has searched through all the literature on the 
subject and has found records of only three cases wheie the 
crossing of a white and a negro resulted in black or white 
in the offspring, and has offered further evidence to show 
that such a crossing almost invariably results in a blend. 
The same is true of a great many other characters, and it 
is difficult to understand why certain Mendelians try to 
apply the Mendelian law to these cases.^ It may be because 
they think that in a case of blended inheritance the allelo- 
morphic characters are equally potent, and therefore both 
of them manifest themselves in the offspring. But this 
seems to indicate that unit characters are not as sharply 
distinguished from each other as the Mendelians would 
have us beHeve. 

Because of the exaggerated claims of some of the Mende- 
lians, it is well to note carefully just what MendeHsm has 
taught us. In the first place, Mendelism throws no direct 
light upon the nature of the germ cell, though it may in- 
directly be of great assistance in criticizing certain of the 
theories as to the nature of the germ cell. For example, 
inasmuch as the Mendehan law seems to indicate the exist- 
ence of unit characters, it gives valuable support to micro- 
meric theories of the nature of the germ cell. Furthermore, 
Mendelism does not postulate discontinuous variations or 
reveal their causes. So far as I know, nowhere in his writ- 

1 Biometrika, Vol. VI, pp. 348-353 (Nov., igio). 

*C. B. Davenport has made experiments which he thinks prove that the color 
of the mulatto is not a blend. See Am. Naturalist, Vol. xlv (191 1). 



The Anatomical and Physiological Basis 59 

ings did Mendel express a belief in such discontinuous varia- 
tions, though they seem to imply such a belief. It has been 
suggested by Bateson that mutations may be recessives 
appearing after a crossing, but if this be the case, it would 
seem as if they were not mutations or discontinuous varia- 
tions at all, but simply reappearances of ancestral charac- 
ters. Nothing new, therefore, could arise as the result of 
the reappearances of these ancestral characters except as 
new combinations of them constitute new types. 

Bateson has also attempted to explain reversion by means 
of MendeHsm. He speaks as follows: ^^ Reversion occurs 
when the sum total of the factors returns to that which it 
has been in some original type. Such a return may be 
brought about by the omission of an element or elements, 
as when the rose-comb fowl for any reason has a single- 
combed offspring. Conversely, the return may occur by 
the addition of some missing element needed to complete 
the original type. As yet no means are known by which 
the omission or addition of elements can be made at will, ex- 
cept by crossing. Reversion on crossing is thus the partic- 
ular case in which one or more missing factors are brought 
in by the parents of the cross-bred. The most striking 
cases of such reversion on crossing are those in which neither 
parent seems to the observer to contain anything specially 
reminiscent of the original type, and yet the offspring of 
the cross are all of that type." ^ It may well be that these 
cases which result from hybridization and which Darwin 
called '^reversion on crossing" can be explained on Mende- 
Uan grounds. But de Vries calls them cases of "false 
atavism or vicinism^' which are due to crossing. He be- 

1 Bateson, op. cit., p. 279. 



60 The Science of Human Behavior 

Keves that most cases of apparent reversion are due to 
crossing and that "true atavism, or reversion caused by an 
innate latent tendency, seems to be very rare." ^ The 
MendeHans have not yet explained the cases of true re- 
version. It is quite possible that the idea of unit characters 
is needed to explain reversion, but these unit characters 
do not act in cases of reversion necessarily in accordance 
with the MendeUan law. 

Galton 

It has been claimed by Bateson and other Mendelians 
that Galton's law of ancestral inheritance is nullified by 
the Mendelian law. Galton's law was to the effect that an 
individual inherited on the average one fourth of his char- 
acters from each parent, one sixteenth from each grand- 
parent, one sixty-fourth from each great grandparent, etc., 
so that the sum total of these ancestral contributions would 
amount to unity. The MendeHans have pointed out that, 
for example, in a case of exclusive inheritance an individual 
may inherit all his characters from and through one parent 
so that the other parent will not be represented at all in 
his inheritance. Thus Galton's law is not a physiological 
formula which can be appHed in every individual case. 
The Galtonians have, however, asserted that even though 
it may not be a physiological formula, it is still a statistical 
formula which applies on the average to a large number of 
generations breeding freely. But it is contended by Bate- 
son that the discovery of the fact of segregation has de- 
stroyed the utility of Galton's law as a statistical formula 
also. ''At the time that Galton's views were promulgated, 

iDe Vries, op. cit., pp. 187-188. 



The Anatomical and Physiological Basis 61 

nothing was known of segregation. The supposition that 
any individual, whatever its own characters, was capable 
of carrying on and transmitting to its posterity any of the 
characters exhibited by its immediate progenitors, at all 
events, was generally received without question by biolo- 
gists. According to that idea the number of classes of in- 
dividuals differing in respect of their ancestral composition 
and transmitting powers is to be regarded as indefinitely 
large, whereas in all cases of sensible allelomorphism the 
number of classes of individuals is three only, two being 
homozygous and one heterozygous. The difference between 
the two schemes is thus absolute and irreconcileable." ^ 
It may well be that the proportion between the average 
contributions of the different ancestors is not correct as 
stated by Galton. As a matter of fact, his leading disciple, 
Karl Pearson, has proposed a different ratio. But I be- 
lieve that the law of ancestral inheritance is true to this 
extent, that the more distant the ancestors, the less the 
resemblance tends to become between them and their de- 
scendants. This is true if for no other reason because the 
more distant the ancestors, the more time there has been for 
variations and mutations to arise which will lessen their 
resemblance to their descendants. It is therefore useless 
for the MendeHans to deny entirely Galton's law as a 
statistical formula, however successful may be their 
criticism of it as a physiological formula. They are, how- 
ever, right in denying that it is a law of inheritance, for it 
does not describe how inheritance actually takes place in 
a single case, but merely indicates some of the results of in- 
heritance in a large number of cases. 

1 Bateson, op. ciL, p. 127. 



62 The Science of Human Behavior 

I do not know whether the Mendelians have attacked 
Galton's law of filial regression, but it seems as if they 
would attack this law also on the same grounds upon which 
they have attacked the law of ancestral inheritance. The 
law of fiUal regression as stated by Galton was to the effect 
that children tend to approximate the mean or average of 
the stock more closely than their parents. The Mende- 
Hans might point out that inasmuch as this is not necessarily 
true in any individual case, this law is not a physiological 
formula any more than the law of ancestral inheritance. 
They might also attack it as a statistical formula on the 
ground that in cases of segregation there is no regression 
to the characters of the average of the ancestors. It is 
evident that Galton's law is simply another way of stating 
the familiar statistical law that any group of phenomena 
tend to approximate a normal mean or average, which can 
be represented graphically by the normal curve of frequency. 
Thus in any stock which is fairly stable its members will 
tend to approximate the mean or average of that stock. 
But it must be noted that in order that there shall be re- 
gression towards the mean, there must already have been 
at least as much digression from it. And in order that 
there shall be any change in the type or species, there must 
be at least a little more digression from the mean than there 
is regression towards it. The law of fiHal regression is, 
therefore, not very illuminating and is perhaps even some- 
what misleading, inasmuch as it takes no note of the di- 
gression from the mean of the stock which must precede 
and accompany regression towards this mean. 

The attitude of the Mendelians towards Galton's law of 
ancestral inheritance illustrates their tendency to depre- 



Th^ Anatomical and Physiological Basis 63 

date greatly the value of statistical methods of studying 
variation and inheritance in favor of their own experimental 
methods. It is true that their experimental methods can 
be used in a great many places where statistical methods 
are not applicable. But it is useless to deny that in the 
study of biological phenomena, as of any other natural 
phenomona where there are a large number of cases 
to be investigated, the statistical method is the only 
feasible one. Furthermore, the statistical method is quite 
as experimental and inductive as that of the Men- 
delians. 

The preceding instance illustrates the tendency on the 
part of certain MendeHans, as, for example, Bateson and 
his followers, to exalt MendeHsm to an unwarranted degree. 
To claim that MendeHsm supplants Darwinism in any sense 
is entirely unjustifiable, while it certainly is preposterous 
to make any personal comparison between Mendel and 
Darwin which is in favor of Mendel, for, however much his 
theories may be disproved by the progress of biology, Dar- 
win still remains the preeminent figure in biological science. 
As we have already seen, and as is admitted by the Mende- 
Hans themselves, MendeHsm explains the origin and causes 
of variation no more than Darwinism. While it denies 
that selection is a cause of variation, it does not deny the 
potency of natural selection in determining the survival 
or extension of variations, as is indicated by Bateson him- 
self in the following words: ''There is also nothing in 
MendeHan discovery which runs counter to the cardinal 
doctrine that species have arisen 'by means of Natural 
Selection, or the preservation of favored races in the struggle 
for Hfe,' to use the definition of that doctrine inscribed on 



64 The Science of Human Behavior 

the title of the Origin. By the arbitrament of Natural 
Selection all must succeed or fail." ^ 

It may further be pointed out that much that is discussed 
under the head of Mendelism is not pecuKarly MendeHan. 
For example, we have seen that there have been numer- 
ous micromeric theories of the germ cell which postulate 
the existence of unit characters. A comparison has been 
made between Weismannism and Mendelism. It is evident 
that the determinants of Weismann are similar to the unit 
characters of Mendel. The purity of type which according 
to Mendelism results from segregation, according to Weis- 
mann is wrought out by a process of germinal selection. 
The dominant character of MendeHsm may prove to be 
the stronger determinant of Weismann which succeeds in 
getting a larger share of nutriment in the intragerminal 
struggle. 

Pure Lines 

In this connection it may be well to speak of the theory 
of pure Hues. A pure line consists of all the descendants 
of a single individual where the mode of reproduction has 
been by self-fertilization. Johannsen has studied the pure 
lines of barley, beans, and other plants and has found that 
in the inheritance of quantitative characters, as, for example, 
the weight of seeds, a pure line has a normal variability of 
its own. That is to say, the members of a pure line do not 
tend to revert to the mean of the general population from 
which the original self-fertiHzed ancestor of the pure line 
was taken, but tend to fluctuate around this individual 
ancestor as a mean. It has been found that the selection 

* op. cit., p. 289. 



The Anatomical and Physiological Basis 65 

of fluctuating variations within a pure line is not effective, 
but that the selected individuals tend to revert to the 
mean of their line. This would seem to furnish further 
evidence against the Darwinian theory of the selection 
of fluctuating variations as a cause of organic evolution. 
Furthermore, it raises the question of the mutability of 
unit characters. De Vries and others have laid great em- 
phasis upon the immutabiHty of unit characters. Morgan 
discusses this question as follows : — 

" De Vries assumes that transitions between unit characters exist 
as little as between the molecules of chemistry. It cannot be main- 
tained, I think, from the evidence that we possess, that unit charac- 
ters are immutable, for there are some cases in which it appears that 
the unit characters may be halved by every crossing. It is true that 
some of these cases may be explained by antagonistic characters both 
developing and mutually influencing the result ; but if they do not 
subsequently separate, it is impossible to tell whether or not a new 
unit character has been formed by combination. Cases of blended 
inheritance especially seem to come under this heading. But so long 
as we do not know definitely what occurs in these cases, it seems to 
me arbitrary to speak of unit characters as immutable and quite un- 
necessary to make this idea a cardinal point of the mutation theory. 
The behavior of certain characters in heredity shows that they do 
act as units, and it is a great convenience to deal with them as such, 
but unnecessary to push the matter so far as to hold that they are 
immutable. If unit characters can be halved, altered, added to, or 
changed in any way, their immutability does not seem to be an es- 
sential point of their characterization, and, as has been said, there is 
some evidence to indicate that such changes may take place. "^ 

Sex Determination 

The idea of unit characters has recently played an im- 
portant part in the study of the determination of sex. For 
a long time the question of how sex is determined has been 

1 T. H. Morgan, Experimental Zoology, New York, 1907, pp. 167-168. 



66 The Science of Human Behavior 

of great importance in biology. Many theories of sex 
determination have been formulated. One of the oldest 
theories has been that sex is determined by the nutriment 
of the parent or of the germ cells themselves. Other 
theories have been that it is determined by the age of the 
parents or by their vigor. Some theories have been based 
upon the condition of the germ cells. It has been claimed 
by some that in the case of certain mammals if the egg is 
fertilized soon after leaving the ovary, it tends to produce a 
female ; if not fertiUzed until later, it tends to produce a 
male. Some have thought that in certain species the size 
of the egg is correlated in some way with sex, the large eggs 
producing females and the small ones males. It has been 
contended that sex is determined by the ratio of the 
nucleus to the cytoplasm. I cannot stop to discuss these 
theories, however interesting they may be, but wish to speak 
briefly of this idea of sex as a unit character which is now 
attracting a great deal of attention in biology. In most of 
the theories which have been mentioned the sex is not 
necessarily determined at the beginning of the life of the 
individual, namely, at the moment of conception, and the 
sex is not entirely determined within the germ cell. But 
according to the theory that sex is a unit character, it is 
determined at the moment of conception and entirely within 
the germ itself, no external forces playing a part in such 
determination. 

This theory has grown out of the discovery of the so- 
called accessory or X chromosome, which seems to be the 
sex determinant in certain species. The chromosomes are 
minute particles of chromatin in the nucleus of the dividing 
germ cell which it has been thought are the bearers of unit 



The Anatomical and Physiological Basis 67 

characters. There is a fixed number of these chromosomes 
for each species. But it has been found in certain species 
that half of the spermatozoa contain one chromosome less 
than the usual number for the species. Just before fer- 
tilization the number of chromosomes in both the egg and 
the sperm is reduced to half in the course of the process 
which is called the maturation of the germ cell. When 
fertilization takes place, the chromosomes of the egg and of 
the sperm are combined, and thus the fertilized germ cell 
contains the full number of chromosomes. If the sperm 
contains the accessory chromosome, the offspring will be 
female ; if the accessory chromosome is absent, the offspring 
will be male. Thus the accessory chromosome seems to 
carry the character of femaleness, and the sperm cells may 
be classified as male or female producing according to the 
sex which they determine. It has also been thought that 
a similar classification could be made of the egg cells. This 
theory seems to explain the average equahty between the 
sexes which has so far been very difficult to explain. Some 
of the Mendelians have taken up this theory and have 
claimed that sex is an allelomorphic unit character. The 
sexual individual would then be a MendeHan hybrid ex- 
hibiting in itself one sex, but carrying the potentiality of 
the other sex. 

The theory that sex is a distinct unit character seems, 
however, to be contradicted by the fact that there are mixed 
sexual individuals known as gynandromorphs. Such cases 
appear most frequently among insects where an individual 
may display male characters on one side of the body and 
female characters on the other, or where the anterior end 
of the body is male and the posterior end female. Among 



08 The Science of Human Behavior 

plants a fully formed stamen sometimes appears upon a 
female flower. Functional mammary glands sometimes 
appear in the male mammal. These facts seem to indi- 
cate that there may be a mixing of sexual characters and 
that sex is not a distinct unit character, as is assumed by the 
above theory. At any rate, it is probable that sex is deter- 
mined in different ways in different species. So that while 
sex may be determined morphologically in certain species, 
as is assumed by the unit character theory, it may be deter- 
mined physiologically in other species by the general con- 
dition of the organism at the time of fertiHzation or shortly 
after. 

Biological Foundation for the Study of Behavior 

I have briefly surveyed some of the most important 
problems in biology to-day. The ultimate object of the 
study of each one of these problems is the explanation of 
the organic evolution now going on. The final explanation 
of this organic evolution must include a synthesis of the 
internal, orthogenetic forces of the organism and the ex- 
ternal, environmental forces. The characters of an or- 
ganism are determined initially by these internal forces. 
But whether or not a given individual or type is to survive 
and perpetuate itself depends upon these external forces 
which are always acting selectively upon all living organ- 
isms. Thus through the elimination of those not fitted to 
their environment, and a survival of those who are fitted, 
adaptation takes place. The raw material for organic 
evolution is furnished by the variations which take place 
within the organism. The greatest need to-day in biology 
probably is the study of the causes of these variations. 



The Anatomical and Physiological Basis 69 

Some of these variations arise out of the internal conditions 
of the organism and do not resuh, at any rate directly, from 
the forces of the environment. Many other variations, 
however, are undoubtedly the direct result of external en- 
vironmental forces, and there is great need for the experi- 
mental and statistical study of the effect of these forces 
upon the organism in causing variations. 

This brief description of the evolution of structural forms 
and physiological processes furnishes the necessary biologi- 
cal foundation for the study of the evolution of behavior. 
It also furnishes the necessary biological basis for psychology 
and sociology, for, as we have seen, mental and social evolu- 
tion consists in large part, if not entirely, of the evolution 
of behavior. It ought not to be necessary to prove that 
psychology and sociology must be based upon biology. In 
the first place, it is evident that there could have been no 
mental and social evolution had there been no organic 
evolution, for, so far as we know, mental and social phe- 
nomena characterize living organisms alone. Furthermore, 
biological forces are still at work and always will be at work 
in determining mental and social evolution, so that psy- 
chology and sociology can never be divorced from biology. 
In studying mental and social phenomena as evolving out 
of biological phenomena, and as being, broadly speaking, 
biological phenomena, we are using the genetic method. 
Not until the genetic method has been in large part sub- 
stituted for the systematizing and classificatory method 
which has so far predominated in psychology and sociology 
can these sciences attain their full development or be gen- 
erally recognized as natural sciences. 

Biology has already played a considerable part in socio- 



70 The Science of Human Behavior 

logical writings. For example, the organic theory of society 
asserted that society is an organism Uke the biological 
organism. But it was soon proved not only that there is 
no identity between society and the biological organism, 
but that there is not even a close analogy between the two. 
The terms heredity, selection, adaptation, and variation 
have played an important part in sociological Kterature. 
But too frequently they have been regarded as distinct 
principles or forces at work in society as well as in the or- 
ganism. For example, it has been asserted that heredity 
is the conservative force in society, while variation is the 
opposing radical force. The preceding discussion has, I 
beHeve, shown that while these terms may describe more or 
less aptly certain processes which are taking place, they 
cannot be regarded as distinct principles or forces in the 
organic any more than in the social world. 

Darwinism is usually assumed nowadays as the biological 
basis in sociological writings. But we have seen that a new 
biology has grown up since Darwin and that many of his 
theories have been disproved, so that it is no longer safe to 
assume Darwinism without qualifications. Some of the 
errors into which sociologists frequently fall have been well 
described by an American biologist : — 

"Much biological sociology rests on two very insecure bases: 
(i) a too slight acquaintance with biology on the part of the biological 
sociologist; and (2) an acceptance of, and confidence in, certain 
biological theories which are certainly unwarranted, and are not at all 
shared by the biologists themselves. Biological science contains much 
that is proved and certain ; but also much that is nothing more than 
working hypothesis, provisional theory, and anticipatory generaliza- 
tion. As the proved part is largely of the nature of facts of observa- 
tion, isolated and unrelated, and the unproved part is composed of 
the large and sweeping generalizations, the plausible, provisional ex- 



The Anatomical and Physiological Basis 71 

planations, such as the various theories of heredity, of the results of 
struggle, of the development of mutual aid, etc., that is, is exactly 
the sort of material that the sociologist needs to weave into his bio- 
logical foundations for the sociologic study of man, it is exactly this un- 
proved part of biology that the searching sociologist carries home 
with him from his excursions into the biological field. The recapitu- 
lation theory looms up large and familiar in biological sociology ; 
it is mostly discredited in biology. The inheritance of acquired 
characters serves as basis for much sociology; most biologists believe 
it impossible. The selection theories are gospel to some sociologists; 
they are the principal moot points in present-day biology. And so on. 
Biology has not yet come to that stage in its development where it can 
offer many solidly founded generalizations on which other sciences 
can buUd. The theory of descent is one such safe great generalization ; 
but perhaps Darwinism is not another. At least many scholars do 
not beHeve that it is." ^ 

The close of the above citation intimates that biology 
has not very much as yet to offer to other sciences. Sociol- 
ogists should, however, make all possible use of present 
biological knowledge and await with great interest further 
biological discoveries. Bateson is more confident of the 
value of present biological knowledge for sociology, his con- 
fidence arising out of his high estimate of the importance 
of Mendelism: — 

" It may be anticipated that a general recognition of the chief 
results of Mendelian analysis will bring about a profound change in 
man's conceptions of his own nature and in his outlook on the world. 
Many have in all ages held the beHef that our powers and characteris- 
tics are directly dependent on physical composition; but when it be- 
comes known that the dependence is so close that the hereditary 
descent of certain attributes can be proved to follow definite predi- 
cate formulae, these ideas acquire a solidity they never possessed 
before, and it is likely that the science of sociology will pass into a 
new phase. The evidence at our disposal already proves that in 
many simple cases of defects and abnormalities the descent is of this 

1 v. L. Kellogg, Darwinism To-day, New York, 1908, pp. 21-22. 



72 The Science of Human Behavior 

definite order, and it is scarcely doubtful that further research will 
reveal comparable examples in abundance. As regards more complex 
phenomena of human inheritance, the descent of characters involving 
the coincidence of several factors, and effects due to interference be- 
tween factors, a complete analysis may be unattainable ; but even in 
some of these more obscure examples a close scrutiny will probably 
discover positive traces of regularity in descent of such a kind as to 
indicate in them also that the bodily or mental characteristic con- 
sidered is a consequence of definite factorial composition. It is not in 
dispute that the appearance or nonappearance of a characteristic 
may be in part decided by environmental influences. Opportunity 
given may decide that a character manifests itself which without 
opportunity must have remained dormant. The question of oppor- 
tunity and of the degree to which the conditions of life are operative 
in controlling or developing characters will some day demand attention, 
but in order to answer such questions successfully it is the first 
necessity that a knowledge of the genetic behaviour of the factors 
should be obtained." * 

The preceding discussion has shown that the whole 
theory of organic evolution must be taken into account by 
psychologists and sociologists, and not merely certain por- 
tions of it, as, for example, the theory of heredity. Men- 
tal and social phenomena have evolved in the course of 
organic evolution, and it is impossible to explain them fully 
except on the basis of the whole theory of organic evolution. 

Biology is of peculiar interest with reference to man. 
It is probable that biological knowledge has not been used 
to the fullest extent in that branch of anthropology which 
deals with the anatomical and physiological characters 
of man, namely, physical or biological anthropology. An- 
thropology is now on a strictly Darwinian basis, but if the 
recent heterogenetic theories are true, man like other species 
may have originated as a mutation. The mutation theory 

> op. cit., p. 303. 



The Anatomical and Physiological Basis 73 

should therefore be thoroughly tested in anthropology. 
In similar fashion the different ethnic types may have orig- 
inated as mutations, so that the mutation theory should 
be appHed to them also in order to test its truth. Most of 
the so-called races of to-day are hybrids, so that the Men- 
delian law may assist us in studying the combinations of 
characters which these races exhibit. All these anthropo- 
logical problems are very difficult, because our knowledge 
of the past is meager and because the human species 
changes very slowly. But the application of these new 
biological ideas to anthropological problems can be made 
with fruitful results, and there is a vast field for the experi- 
mental and statistical study of these anthropological prob- 
lems in which this biological knowledge can be utilized. 

Furthermore, this appKcation of biological knowledge to 
anthropological problems will be of great value to psychol- 
ogy. The researches of Galton, Pearson, and others have 
shown that mental characters are not independent of in- 
heritance. This was in any case a self-evident truth, for 
mental characters are caused by and correlated with biolog- 
ical characters, so it is evident that mental characters must 
be transmitted along with the biological. To trace the 
causal relationship is frequently a difficult thing to do, for a 
distinct mental character does not necessarily arise out of a 
single biological character, but may be caused by the com- 
bination of many biological characters comprising a large 
part or even the whole of the organism. The study of 
these psychological problems on a biological basis will 
undoubtedly help greatly in explaining the differences 
between the mental characters of different races and of the 
two sexes. 



74 The Science of Human Behavior 

So far I have been discussing the significance of biology 
for psychology and sociology and the extent to which bio- 
logical forces have determined mental and social evolution. 
But there has not been sufficient recognition in biology of 
the part that has been played by the mental and social 
forces in organic evolution. For while mental and social 
phenomena arose in the course of organic evolution, they 
have reacted upon organic evolution and have influenced 
it greatly. Some of the students of animal behavior have 
recognized this reaction, and I shall discuss it in later chap- 
ters. 



CHAPTER V 

THE BEHAVIOR OF THE LOWER ANIMALS 

Behavior as the dynamic, functional aspect of external organic 
phenomena, 75. — Application of the genetic method in psychology, 
77. — The genetic method as the phylogenetic method, 77. — The de- 
velopment of the science of behavior by biologists and comparative 
psychologists, 77. — Experimental psychology, 78. — The irritability 
of organic matter arising out of its unstable and mobile nature, 79. — 
Is this irritabiHty a psychic characteristic ? 79. — The direct reac- 
tions of organisms to external forces, 80. — Definition of a tropism, 
81, — The external forces which act upon organisms, 85. 

The last two chapters were in the main morphological 
in their character. That is to say, they dealt with the 
forms and structures of organisms, but scarcely touched 
upon the incessant activities which characterize every or- 
ganism. Organic phenomena were therefore treated in 
large part as if they were static phenomena. To be sure, 
variation and adaptation and the origin and evolution of 
the dififerent species were discussed. But there was little 
indication that these changes resulted in part from the 
activities of the organisms, and the implication seemed to be 
that they were the result of external forces acting upon 
organisms in a passive state. 

This has, I believe, been true altogether too frequently 
of general treatises on biology. There has been little in 
them to indicate that the activities of the organisms them- 
selves have played a part in the organic evolution which 

75 



76 The Science of Human Behavior 

they attempt to describe. This has, however, been far 
less true of treatises on physiology, for in them the activi- 
ties and functions of the organs have necessarily been de- 
scribed so that the study has been much more dynamic in 
its character. 

In the following chapters we are to deal with the d3niamic, 
functional aspect of organic phenomena in the study of 
animal behavior. That such a study is not different in 
kind from physiology is indicated in the following citation 
from one of the leading students of animal behavior: "By 
behavior we mean the general bodily movements of organ- 
isms. These are not sharply distinguishable from the 
internal physiological processes. . . . But behavior is a 
collective name for the most striking and evident of the 
activities performed by organisms." ^ Assuming, therefore, 
that behavior includes the external, more obvious physio- 
logical activities, it is evident that it must have an impor- 
tant morphogenetic role and that organic forms and struc- 
tures must be determined in part by the behavior of the 
organisms they characterize. Modifications of behavior 
must therefore play a part in the modification of mor- 
phological characteristics. "The modifiability of the 
characteristics of organisms has always been a subject of 
the greatest importance in biological science. In most 
fields the study of this matter is beset with great difficulties, 
for the modifications require long periods and their prog- 
ress is not easily detectable. In the processes of behavior 
we have characteristics that are modifiable with absolute 
ease. In the ordinary course of behavior variations of 
action are continually occurring, as a result of many in- 

• H. S. Jennings, Behavior oj the Lower Organisms, New York, 1906, p. v. 



The Behavior of the Lower Animals 77 

ternal and external causes. We see quickly and in the gross 
the changes produced by the environment, so that we have 
the best possible opportunity for the study of the principles 
according to which changes occur. Permanent modifica- 
tions of the methods of action are easily produced in the 
behavior of many organisms. When we Umit ourselves 
to the subjective aspect of these, thinking only of memory, 
or the Hke, we tend to obscure the general problem involved. 
This problem is : What lasting changes are producible in 
organisms by the environment or otherwise, and what are 
the principles governing such modifications? Perhaps in 
no other field do we have so favorable an opportunity for 
the study of this problem, fundamental for all biology, as 
in behavior. There seems to be no a priori reason for 
supposing the laws of modification to be different in this 
field from those found elsewhere. The matter needs to be 
dealt with from an objective standpoint, keeping the general 
problem in mind." ^ Behavior must therefore be studied 
in any complete survey of organic evolution. 

The prime need in psychology to-day is the development 
of its genetic aspect. It is true that there has been a good 
deal written on what is called genetic psychology. But 
most of this has dealt with the psychic evolution of the 
human child alone. Genetic psychology should deal with 
the origin of psychic phenomena in general. In order to 
be thoroughly genetic, psychology must be phylogenetic. 
The evolution of psychic phenomena should be traced from 
the lowest species up to the highest. This work has been 
commenced by the comparative psychologists or students 
of animal behavior. Some of these are biologists and 

^ Jennings, op. cit., p. vi. 



78 The Science of Human Behavior 

zoologists, like Loeb or Jennings, who have been impressed 
with the part played in organic evolution by the activities 
of organisms. Others are psychologists, who have become 
interested in the mental processes of animals other than 
human beings. But the essential truth which most of 
these students of animal behavior have recognized is that 
psychic phenomena cannot be profitably studied except on 
the basis of a knowledge of the objective facts of behavior. 
We cannot pretend to know anything with much certainty 
about the psychic characteristics of any species, not even 
the human species, without being well acquainted with the 
modes of activity of that species. I propose therefore in 
the present and the two succeeding chapters to discuss the 
objective aspects of the behavior of the lower animals, 
relegating the discussion of the psychic or conscious aspects 
of such behavior to later chapters. 

Many of the psychologists are giving their time now to 
experimental psychology. Abandoning the deductive and 
exclusively introspective methods of the older psychologists, 
they are using the inductive, experimental methods of 
modern science. But it is true of these psychologists, also, 
that they are devoting most of their time to the study of 
human beings. It is quite likely that genetic psychology 
will make much of this unnecessary by explaining certain 
phenomena which are now inexplicable and will, further- 
more, show what experiments should be made. 

If genetic psychology is developed as indicated above, the 
genetic method can be applied in psychology and sociology 
as it is now being applied in biology. These two sciences 
are now in much the same position as was biology during 
the Linnean period a century or so ago, namely, in the sys- 



The Behavior of the Lower Animals 79 

tematizing period. The genetic method must be adopted 
before they can pass beyond this period and become full- 
fledged sciences. 

In accordance with the genetic method the simplest re- 
actions must be studied before the more complex. Con- 
sequently we shall discuss the reactions of the simplest 
organisms in this and the two succeeding chapters and take 
up the more complex reactions which characterize the ner- 
vous system, namely, the reflexes and the instincts, in later 
chapters. 

Irritability of Organic Matter 

It is, I think, generally believed that all the activities of 
living organisms arise primarily out of what is usually 
called the irritabiHty of organic matter. I have already 
discussed this characteristic, without, however, mentioning 
its name, in the chapter on the physico-chemical basis of 
life. It arises out of the unstable and mobile nature of 
organic matter. It is at bottom nothing more than the 
facility with which organic matter changes as a result of 
the molecular and molar forces which act upon it. It is 
therefore a characteristic not different in kind, but only in 
quantity, for any matter will change as a result of the action 
of forces upon it. Many psychologists, however, and others 
also, have assumed that irritability is a psychic characteristic, 
and some have seemed to think that it marks an absolute 
distinction between organic and inorganic matter. Many 
illustrations of the behef that irritability is a psychic char- 
acteristic might be cited. For example, a French psycholo- 
gist, Richet, speaks of the irritability of unicellular organ- 
isms as follows: "Irritability is their entire Hfe, but it 



80 The Science of Human Behavior 

is already a psychic life; so that cellular irritability can 
be considered as the elementary psychic Hfe." ^ Another 
French psychologist, Binet, reveals the same belief in a 
book in which he gives an account of the study of the be- 
havior of unicellular organisms which had been made up 
to that time, but to all of which he gives a psychic interpre- 
tation. In the following passage he indicates liis belief 
in the psychic characteristics of single cells and states that 
Haeckel had already revealed such a belief: *'In giving 
to the psychology of these microscopic beings the name of 
cellular psychology, I have not invented a new expression, 
nor given a new sense to an old expression. M. Haeckel, 
a very long time before me, has made a study of cellular 
psychology, and his study rests entirely, Hke mine, upon the 
observation of the animal and vegetable organisms." ^ 

Haeckel seems to think that all matter possesses psychic 
characteristics. I do not know whether Binet is of the same 
opinion or thinks that psychic characteristics mark an ab- 
solute distinction between organic and inorganic matter. 
I think that both opinions are wrong and that psychic 
characteristics first appear in later stages of organic evolu- 
tion. However, we are not concerned ^ith the psydifcin 
this chapter, but are to discuss irritability and the bOTTVIor 
of the lower organisms as purely objective phenomena. 

What, then, are the simplest forms of behavior ? They 
are the direct reactions of organisms to external forces. 
All forms of behavior are in the last analysis reactions to 
external forces. But in the higher organisms these reac- 
tions become more or less indirect. We must therefore 

^ Charles Richet, Essai de psychologic ginirale, Paris, 1887, p. 20. 

• A. Biaet, La vie psychique des micro-organismes, 2d edit., Paris, 1891, p. 231. 



The Behavior of the Lower Animals 81 

discuss first the cases where there is little to complicate 
the directness of the reaction to external forces. 

The Tropism 

Various names have been given to these direct reactions. 
Sometimes more than one name has been given to the same 
form of reaction. The best known of these names is that 
of tropism. A theory of tropisms has been developed which 
has stimulated a great deal of discussion and a good deal of 
difference of opinion. Because of this difference of opinion 
it is difficult to tell just what a tropism is. Let us see what 
are some of the definitions of a tropism. 

A very simple definition of a tropism is the following: 
*'The direct motor response of an animal to an external 
stimulus is known as a tropism, from the Greek word 
meaning Ho turn.'" ^ It is evident that according to this 
definition the term tropism would cover most if not all 
of the direct reactions we have described. This is an 
example of a very broad conception of the meaning of 
tropism. 

The most distinguished exponent of the tropism theory, 
or perhaps I should say, of a tropism theory, is the well- 
known physiologist, Jacques Loeb. His conception of a 
tropism is more restricted and more compHcated than the 
one illustrated above. He speaks of tropisms as follows: 
''These tropisms are identical for animals and plants. 
The explanation of them depends first upon the specific 
irritability of certain elements of the body surface, and, 
second, upon the relations of symmetry of the body. 
Symmetrical elements at the surface of the body have the 

1 Margaret F. Washburn, The Animal Mind, New York, 1908, p. 57. 

G 



82 The Science of Human Behavior 

same irritability ; unsymmetrical elements have a different 
irritability. Those nearer the oral pole possess an irri- 
tability greater than that of those near the aboral pole. 
These circumstances force an animal to orient itself toward 
a source of stimulation in such a way that symmetrical 
points on the surface of the body are stimulated equally. 
In this way the animals are led without will of their own 
either toward the source of the stimulus or away from it." ^ 
Thus we see that Loeb's tropism theory involves several 
things. It involves speciaHzed forms of irritability on the 
body surface of the animal or plant concerned and sym- 
metry of the organism. As a result of these conditions the 
organism is forced to orient itself toward the source of 
stimulation so that these symmetrical points will be stimu- 
lated equally. 

Loeb's tropism theory has aroused a great deal of dis- 
cussion and much disagreement. We find that even some 
of those who proclaim themselves disciples of Loeb do not 
define tropism as he does. For example, Bohn gives the 
following definition : *'I give here to the word tropism the 
meaning that Loeb has attributed to it, and consequently I 
consider it as the simplest act that an animal can present." ^ 
It is evident that this definition does not necessarily involve 
specific irritability, symmetry, or orientation, as does Loeb's 
definition. 

Davenport seems to regard as a tropism any modifica- 
tion of the direction of growth of an organism by an exter- 
nal force, for in the second volume of his work on experi- 

1 Comparative Physiology of the Brain and Comparative Psychology, New York, 
IQOO, p. 7. Cf. Loeb, The Dynamics of Living Matter, New York, 1906, pp. 138-139. 

* Georges Bohn, Lcs tropismes, les reflexes, el I'intelligence, in L'annle psycholo- 
giqtie, edited by A. Binet, Paris, 1906, p. 147. 



The Behavior of the Lower Animals 83 

mental morphology he deals with the '' effect of chemical 
and physical agents upon growth" and each of these modi- 
fications he calls a tropism. In the first volume of this 
work he deals with the '' effect of chemical and physical 
agents upon protoplasm" and discusses most of the time 
the determination of the direction of locomotion of an 
organism by external forces, which he calls "taxis." It is 
evident that this is similar to Loeb's use of the term tropism 
and we shall discuss its meaning shortly. 

Jennings describes the diversity of meanings which have 
been attributed to the word tropism, but believes that one 
meaning is generally accepted. "The word 'tropism' has 
been used in several different senses by different authors, 
and not always as implying a definite theory. But there 
is a certain theory which is usually implied when tropisms 
are mentioned; it has become so generally accepted that 
it is often spoken of as the tropism theory. It will perhaps 
be more accurate to speak of it as the local action theory 
of tropisms." ^ By this he means a tropism theory which 
assumes that external forces determine behavior by affect- 
ing in a different fashion the different parts of the organism, 
and sometimes affecting some parts of the organism not 
at all. Loeb's theory is of this kind, as is indicated in the 
definition which has been quoted in which he says that 
the explanation of tropisms depends upon "the specific 
irritability of certain elements of the body surface." After 
criticizing this local action theory of tropisms (a criticism 
which will be discussed later), Jennings says : "In the fore- 
going pages we have criticized a certain definite theory of 
tropisms, this being the theory most commonly impHed 

* op. ciL, p. 265. 



84 The Science of Human Behavior 

when the word is used in a precisely defined way. But 
the term 'tropism' is often used in a looser sense. By 
some writers the word is applied merely to the general 
phenomenon that the movements of organisms show 
definite relations to the location of external agents." ^ 

Another term which is appHed to certain reactions is the 
word taxis, which is derived from the Greek word meaning 
*'to arrange." By some writers taxis is used in the same 
sense as tropism.^ For example, Verwom speaks as follows : 
" Although the words ' chemotropism,' ' heliotropism,' 
etc., have been long in use, I have decided, after consider- 
able delay, to exchange them in this edition of the book 
for the words 'chemo taxis,' 'photo taxis,' etc.; my reason 
is that the former not only sound heavy, but suggest 
objections from the philological standpoint." ^ He does 
not state what are the philological objections to the term 
tropism, but he evidently thinks that tropism and taxis 
mean the same thing. 

Other writers use the two terms with different meanings. 
*'By some writers the word 'tropism' is restricted to the 
bending or inclination of a fixed organism, while the move- 
ments of free organisms under the influence of external 
agents are called taxis. ^' ^ Davenport would, I think, be 
an example of this class, for, as we have seen, he applies 
tropism to modifications of the direction of growth by 
external forces, which is true principally of fixed organisms 
such as plants, while he appHes taxis to the determination 
of the direction of locomotion by external forces, which 
would be true only of free organisms. 

* Op. cU., p. 274. * Cf. Washburn, op. cit., p. 57 ; Jennings, op. cit., p. 275. 

• Max Verwom, General Physiology, London, iSgg, p. 429. 
♦Jennings, op. cit., p. 275. 



The Behavior of the Lower Animals 85 

Many other terms have been applied to the reactions of 
the lower organisms, such as kinesis, -pathy, -metry, phobism, 
clinism, etc. We shall not stop to define and discuss these 
terms for the following reason: On account of the multi- 
plicity of these terms and the diversity of meanings which 
have been given to them, there has resulted a good deal of 
confusion of thought and the obscuring of the real nature 
of the phenomena involved. We shall therefore use as few 
of these terms as possible and shall devote ourselves rather 
to the study of the reactions themselves. The attempt to 
devise a technical nomenclature for these reactions is a 
commendable one, for it arises out of the desire to describe 
these phenomena in as precise and objective terms as pos- 
sible. But, as Jennings says, "the study of behavior 
seems hardly to have reached as yet the stage where a 
hard and fast nomenclature can be used to advantage. 
To the present writer, after a long-continued attempt to 
use some of the systems of nomenclature devised, descrip- 
tions of the facts of behavior in the simplest language pos- 
sible seems a great gain for clear thinking and unambiguous 
expression." ^ 

External Forces as Stimuli 

We shall turn now to the study of the reactions of the 
simplest organisms to external forces. What are these 
forces? Davenport classifies them as follows: "These 
may be grouped into eight categories, determined largely 
by convenience; namely, i, chemical substances; 2, water; 
3, density of the medium; 4, molar agents; 5, gravity; 
6, electricity; 7, light; and 8, heat." 2 

1 op. cit., p. 276. » Op. cit., p. viii. 



86 The Science of Human Behavior 

Verworn gives a somewhat briefer classification of these 
external forces which he calls stimuH. First he defines 
a stimulus as follows: **A stimulus may be defined as 
e^ery change of the external agencies that act upon an organ- 
ism. If a stimulus comes in contact with a body that 
possesses the property of irritability, i.e. the capabiHty of 
reacting to stimuli, the result is stimulation.^^ ^ Then he 
discusses the varieties of stimuli as follows: "If every 
change of the agencies that act upon the organism from 
without is able to stimulate, it is evident that innumerable 
kinds of stimuli exist. Not only may every existing con- 
dition of Hfe be changed, but new conditions may appear 
and affect the organism. Notwithstanding this possibility, 
stimuli may be classified according to their quaUties into a 
few large groups. A natural classification is possible in 
accordance with the forms of energy which the different 
stimuh represent; for the operation of every external 
agent upon a body depends upon a transformation of 
energy. In accordance with this principle, all influences of 
a chemical nature may be grouped as chemical stimuli^ in- 
cluding not only changes in the income of food, water, and 
oxygen, but other chemical changes which ordinarily do 
not come into contact with the organism. ... All purely 
mechanical influences that affect the organism may be 
termed mechanical stimuli, including those that consist in 
changes of pressure, such as pushing, shaking, pressing, 
pulling, and sound vibrations, those that manifest them- 
selves by molecular attractions, such as cohesion or ad- 
hesion in the surrounding medium, and those that depend 
on the action of gravitation. Thermal stimuli comprise 

» op. cit., p. 348. 



The Behavior of the Lower Animals 87 

changes of the temperature that surrounds the organism. 
Photic stimuli comprise changes of light. Electrical stimuli 
comprise electrical changes. ... Stimuli, therefore, com- 
prise chemical, mechanical, thermal, photic, and electrical 
changes in the environment of the organism, and no others." ^ 
These two classifications are sufficient to suggest the 
forces which act upon organisms and we shall now turn to 
the study of the behavior which results from such action. 

1 op. cit., pp. 348-349- 



CHAPTER VI 

TROPISMS 

Phototropism, 88. — Photopathy, 92. — Does the direction or the 
intensity of the rays of light determine the reactions of organisms to 
light? 93. — Positive and negative phototropism, 95. — Is the action 
of hght on organic matter mechanical or chemical ? 99. — Chromo- 
tropism, 102. — Rudimentary vision, 105. — The utiHty of reactions 
to light, 105. — Geotropism, 107. — The force of gravity, 108. — 
Chemotropism, 109. — Rudimentary senses of smell and taste, iii. — 
Galvanotropism, 112. — Barotaxis, 113. — Stereotropism (thigmo- 
tropism) or contact irritability, 113. — Rheotropism, 114. — Anemo- 
tropism, 116. — Thermotropism, 116. — Hydrotropism, 116. — Tono- 
tropism, 116. 

The first group of reactions to external forces I shall 
discuss is that of reactions of organisms to light.^ Organ- 
isms are being subjected to Kght pretty constantly, and 
their reactions have been studied a great deal, so that the 
reactions of organisms to external forces are well illus- 
trated in this group. 

Phototropism 

It has long been a well-known fact that certain plants 
turn their flowers, leaves, etc., towards the sun or any 
other source of Hght, while other plants turn away from 
Hght. Such reacting to Hght has long been called ftelio- 
tropism, a word derived from the Greek words for "sun" 
and "to turn." When the turning is towards the source 

* Since the present chapter was written there has appeared an excellent summary 
of this subject in S. O. Mast, Light and the Behavior oj Organisms, New York, igii. 

88 



Tropisms 89 

of light, it is called positive heliotropism ; when it is away 
from the light, it is called negative heliotropism. It has 
also long been known that certain of the lower organisms 
react in similar fashion towards light, as, for example, the 
moth, which flies towards a source of light, such as a flame, 
and the earthworm, which crawls away from the sunlight. 
Various anthropomorphic interpretations of such phe- 
nomena have been offered, as, for example, that a plant 
turns towards the light because it loves the Hght and that 
a moth flies into a flame out of curiosity. For a long time, 
however, the reactions of plants and of animals to Hght were 
not identified as being the same. It goes without saying 
that these anthropomorphic explanations are not tenable, 
and I shall now discuss more scientific explanations of 
these reactions. 

But first a word must be said with regard to nomen- 
clature. Strictly speaking, the word *' heliotropism" refers 
only to reactions to sunHght. This fact has encouraged 
the introduction of special terms, such as " selenotropism, " 
or turning towards the moon. To be sure, heliotropism has 
been used in the broad sense of a reaction to all kinds of 
light, as, for example, by Loeb. But the term ^'photo- 
tropism" has been devised, which expresses this broad 
sense very well and which I shall therefore use. The term 
"photo taxis" is also used by some in this same broad 
sense, though usually the meaning of this term is somewhat 
restricted in other respects. 

The reactions of plants to light have been studied for a 
long time, and it has long been recognized that the curva- 
ture of plants in response to Hght is the result of imequal 
growth. "It is clear that photo tropic curvature, as seen 



90 The Science of Human Behavior 

in the seedling, the mold, or the hydroid, is the result of 
unequal growth upon the two sides of the cyUndrical 
organ; and, indeed, that the positive phototropism is due 
to a relative diminution of growth on the side next the 
source of Hght, and the negative phototropism to a rela- 
tive increase of growth on that side. Experiments have 
shown that in positive phototropism growth is excessively 
rapid upon the convex side of the organ, and excessively 
slow upon the concave side. These results are reasonably 
attributed to an increased turgescence on the one side and 
a decreased turgescence on the other." ^ 

Some of the earlier investigators of heliotropism in plants, 
such as von Sachs ^ and Strasburger,^ beHeved that the 
orientation of plants towards the sun was determined by 
the direction of the rays of light and their refrangibility. 
Loeb conducted some experiments which, he believed, 
proved that the reactions of the lower animals to light are 
determined in the same way. *'In a former paper I showed 
that the dependence of animal movement upon light is 
identical with that of plants on the same source of stimu- 
lation. I showed that the law put forward by Sachs for 
the heliotropism of plants, namely, that the direction of 
the rays of Hght determines the orientation, holds good 
also for animals. Free-moving animals are compelled to 
execute their progressive movements in the direction of the 
rays of light, as is the case with the swarm spores of certain 
Algae. It was further proved that the more refrangible 

1 C. B. Davenport, Experimental Morphology, New York, iSgg, Vol. II, pp. 

444-445- 

2 J. von Sachs, Vorlesungen iiber Pflanzen-Physiologie, 2d edit., Leipsic, 1887. 
> E. Strasburger, Wirkung des Lichles und der Wdrme auj Schw&rmsporen, 

Jena, 1878. 



Tropisms 91 

rays of the visible spectrum are the rays that are solely, 
or at least chiefly, effective in bringing about the move- 
ments of these animals ; as is the case in the heliotropic 
movements of plants." ^ 

But many investigators of the subject have denied that 
the direction of the rays of light determines the movements 
of organisms, but that on the contrary it is the intensity 
of the light. For example, Verworn has opposed Loeb's 
theory, as is indicated in the following passage : "From the 
preceding consideration and by analogy with the directive 
effects of other stimuH it is evident that only the differ- 
ence in the intensity of the light upon different parts of 
the body can produce a directive effect ; where the stimu- 
lus acts upon the surface of the body from all sides with 
equal intensity, the reason for a definite axial position dis- 
appears, as is to be observed most clearly in the action of 
chemical stimuli upon all sides. Although this is obvious, 
some investigators, such as Sachs and Loeb, have believed 
that the direction of the rays is more responsible for the 
manifestation of phototactic phenomena than are differ- 
ences in intensity. It is difficult to conceive this, for, 
since the assumption of an axial direction is possible only 
when differences exist at two different points of the surface 
of the body, it is wholly mystical how the directions of 
the rays, which is the same on all sides of the body, can 
produce such an effect." ^ 

It is true that Loeb also had recognized the reactions of 
organisms to differences in the intensity of light, as he 

1 Pflugers Arckiv, Vol. XL VII (1890), p. 391, translated in Studies in General 
Physiology, Chicago, 1905, Vol. I, p. 89. 

2 Max Verworn, General Physiology, London, 1899, pp. 450-451. 



92 The Science of Human Behavior 

insists in the following passage: ''I showed first, that the 
orientation and the direction of the progressive motion of 
certain animals can be controlled unequivocally by the 
direction of the rays emanating from a source of Hght, 
and I showed, moreover, that this type of reaction is, as 
far as we can judge, in every point identical with the 
heHotropic reaction of plants. A few years later I showed 
that there exists another group of animal reactions to light, 
which is not covered by the theory of tropisms, but which 
depends upon the rapidity of the change of the intensity 
of the hght. This latter type of reaction I designated 
as Unterschiedsempfindlichkeit.^'' ^ However, this passage 
seems to indicate that Loeb still beHeves that some at 
least of the reactions of organisms are determined by the 
direction of the rays of Hght. 

Reactions determined by the direction of the rays of 
light have sometimes been called phototaxis, and those 
determined by the intensity of light photopathy. Daven- 
port defines these terms as follows: "In this section we 
shall deal with two sets of phenomena which very Hkely 
are different, but which, in our ignorance, we cannot al- 
ways distinguish. The first includes that active migra- 
tion of organisms whose direction is determined by that 
of the rays of light. This is phototaxis. The second in- 
cludes the wandering of organisms into a more or less 
intensely illuminated region, the direction of locomotion 
being determined by a difference in intensity of illumina- 
tion of the two poles of the organism. This is photop- 
athy." 2 

* Concerning the Theory of Tropisms, in the Jour, of Experimental Zoology, Vol, 
IV, p. 151 (Feb. 1907). 

' C. B. Davenport, Experimental Morphology, New York, 1897, Vol. I, p. 180. 



Tropisms 93 

There has been a long controversy over this question as 
to whether the reactions of organisms to Hght are deter- 
mined always by the intensity or sometimes by the direc- 
tion of the rays of light. It is possible that the direction 
of the rays has an effect in orienting the organism, but the 
weight of opinion now seems to be that it is the intensity 
which always determines it. The direction does, to be 
sure, have something to do with it, because the intensity 
of the light at different points on the body is determined 
by the direction from which the light is coming. But it 
is the intensity which determines the activity of the dif- 
ferent parts of the body. That is to say, if an organism 
is symmetrical so that corresponding points on the two 
sides of the body are equally sensitive to the light, and if 
the light is coming from one side, the other side will be in 
the shade and will therefore not be as intensely illumi- 
nated as the first side. Under such conditions the muscles 
or other locomotor organs on the light side will probably 
be stimulated to greater activity, so that the organism will 
be pulled around into a position parallel with the rays of 
light. In such a case it might easily appear as if the orien- 
tation was being effected by the direction of the rays of 
light, whereas in reality it was caused by the unequal in- 
tensity on the opposite sides of the body. If this theory 
is true, there is little if any difference between photo taxis 
and photopathy. In both cases the intensity of the Hght 
is the final cause of the reaction. In the first case the 
organism is definitely oriented with respect to the source 
of the light, while in the second case it would not be defi- 
nitely oriented. Phototaxis would then exist when the 
light was coming from one direction, while photopathy 



94 The Science of Human Behavior 

would exist when the light was evenly diffused. In the 
second case the organism would be restless, and the orien- 
tation would be effected by wandering about until it came 
into a region of different intensity. If the intensity in 
this region was greater, the organism would remain there 
if it was positively photopathic. If it was negatively pho- 
topathic, it would not come to rest until it reached a region 
of less intensity. 

Holt and Lee ^ made some experiments to test this theory 
and came to the conclusion that there is no difference be- 
tween phototaxis and photopathy. I have not sufficient 
space to give a full account of their investigation, but can 
only quote their conclusions. ''The direction of the rays 
has, in itself, no effect whatsoever on movements of organ- 
isms. It is true, however, that if the rays reach the animal 
from a certain side, that side of the body is stimulated more 
than the other, for the other side lies in its own shade." ^ 
"Light acts in one way, that is, by its intensity. The light 
operates, naturally, on the part of the animal which it 
reaches. The intensity of the light determines the sense 
of the response, whether contractile or expansive; and 
the place of the response, the part of the body stimulated, 
determines the ultimate orientation of the animal."^ ''A 
given portion of an organism stimulated by a given inten- 
sity of light will respond, so far as is shown by the facts 
hitherto observed, by orienting the organism in a particular 
way. The facts do not show that the direction of the ray 
is otherwise effective than in determining on what part of 
the animal the light shall fall. There is no evidence that 

* E. B. Holt, and F. S. Lee, The Theory of Phototactic Response, in the Am. Jour, 
of Physiology, Vol. IV, pp. 460-481 (Jan. 1901). * P. 480. • Pp. 480-481. 



Tropisms 95 

organisms respond to any other property of light than its 
intensity, and the distinction commonly made between 
phototaxis and photopathy as different forms of irritability 
is unwarranted." ^ 

Jennings ^ also has made some experiments which throw 
light on this subject. He chose for his experiments two 
species of the protozoon group, infusoria. One of them was 
the Stentor coeruleus, which reacts negatively to Hght. This 
is an unsymmetrical organism which propels itself by means 
of cilia. He foimd that the stentors swim about in all 
directions in the dark. But as soon as one of them comes 
to the lighted area it at once reacts by what he calls the 
'^avoiding reaction." That is to say, it swims backward 
and turns toward the right aboral side. Then it moves 
forward on a new course. If this again brings it into the 
Hght it gives again the avoiding reaction and continues to 
do so until it no longer comes into the light. This is what 
Jennings calls the "method of trial" which he believes 
characterizes much of the behavior of the lower organisms. 
This will be discussed in the next chapter. He beHeves 
that the stentor responds with this avoiding reaction to 
light because its anterior, oral end is very sensitive to light 
so that it is forced to withdraw its head from the light. 
It does not turn and swim parallel with the rays of light, 
so that its orientation is not determined by the direction 
of rays of light. "The orientation of the free Stentor in 
line with the light rays, with its anterior end directed away 
from the source of light, is due to the fact that an increase 
of illumination at the sensitive anterior end induces the 
avoiding reaction. As a necessary result the oriented 

1 p. 481. 2 Behavior of the Lower Organisms, New York, 1906, pp. 128-141. 



96 The Science of Human Behavior 

S ten tor, swimming in a spiral path, tries new directions of 
movement until it finds one where such changes of illumina- 
tion no longer occur. Such a direction is found only in 
orientation with the anterior end directed away from the 
source of light." ^ 

Loeb, who, as we have seen, is the leading exponent of 
the tropism theory, has pointed out ^ that he had recognized 
long ago this type of reaction to light and had described 
it in the case of planarians and earthworms. ''Such ani- 
mals become more quiet when the intensity of light is 
rapidly diminished, become more active when the intensity 
of Hght is suddenly increased. The consequence is that 
places of a relative minimum in the intensity of light act 
like a trap upon them." ^ He insists, however, that the 
existence of these cases of Unierschiedsempfindlichkeit, as 
he calls them, or of photopathy, as they have been called 
by others,^ does not disprove the existence of the cases 
where the reactions are determined by the direction of the 
rays of light. 

The other species of infusoria which Jennings chose for 
experiment was the Euglena viridis, which reacts positively 
to Hght. This is a relatively unsymmetrical organism which 
propels itself by means of a flagellum fastened at its ante- 
rior end. Near the anterior end it has a red pigment spot 
known as the eye spot. Because of its unsymmetrical 
shape it swims in a spiral course. Euglenae gather in 

^Op. cit., p. 134. 

2 Concerning the Theory of Tropisms, in the Jour, of Experimental Zoology, Vol. 
IV, p. iss (Feb, 1907). ' Op. cit., p. 155. 

* This response to changes in the intensity of light has also been called "reaction 
to change" by Jennings, in the Jour, of Comp. Neurology and Psychology, Vol. XIV, 
pp. 464-468 (1904), and "sensibility diff^rentielle" by Georges Bohn, La nouvelU 
psychologic animale, Paris, 191 1. 



Tropisms 



97 



niL... 



lighted areas where the light is not too strong. If one of 
them swims into a dark region, it immediately gives the 
avoiding reaction and moves forward in another direction. 
If this again brings it into the dark, it gives the avoiding 
reaction again and continues to do so until 
it moves forward into the light. If light 
is thrown upon it from one side, it does 
not turn immediately towards it. But 
as it swings to the right and to the left in 
its spiral course it will tend to swing more 
towards the source of the light than it will 
in the other direction. ^' The result is that 
in its spiral course it successively swerves 
strongly toward the source of Hght, then 
slightly away from it, until by a contin- 
uation of this process the anterior end is 
directed toward the Kght. In this posi- 
tion it swims forward." ^ Jennings con- 
tends that this reaction is entirely the 
result of the effect of the intensity of the fig 
light on the sensitive oral end of the or- 
ganism. But it is true that this reaction 
has the appearance of being determined 
by the direction of the rays of hght, and 
consequently Jennings has been criticized 
for this explanation of it. For example, Torrey has claimed 
that this is a case of a reaction being determined by the 
direction of the rays. In an extended criticism of Jennings 
he speaks as follows: ^'It is hard for me to conceive how 
an organism swimming of necessity in a spiral course could 

1 op. cit., pp. 13&-139. 




I. — Euglena viri- 
dis. C.V., reservoir of 
the contractile vacu- 
ole; e, eye spot; g, 
gullet; nu, nucleus; 
X, larger or upper lip. 
(From Jennings, after 
Kent.) 



98 The Science of Human Behavior 

react more definitely to a moderate directive stimulus than 
does Euglena here." ^ Jennings has replied to this criticism 
by saying ^ that in this experiment when the organism is 
subjected to light from one side, the swinging in the spiral 
course increases towards both sides, but it increases more 
towards the Hght, and this is why it becomes oriented in 
course of time towards the source of Hght. He contends 
that the increased swerving towards the Ught can be ex- 
plained as a tropic reaction, but that the increased swerving 
away from the light cannot possibly be explained by the 
tropism theory. So he concludes that the orienting is 
accompHshed entirely by the intensity and not at all by 
the direction of the light. 

Jennings' conclusion from these two experiments reads 
as follows: ^'Thus in both negative organisms (S ten tor) 
and positive organisms (Euglena), the determining cause 
of the reaction is a change in the intensity of light, and the 
reaction takes place by the usual method of the performance 
of varied movements, subjecting the animal successively 
to different conditions. When the sensitive anterior end 
is subjected alternately to light and shade, the organism 
' tries ' other directions of movement till it finds one where 
such changes are not produced. In Stentor it is an in- 
crease of Hght that causes this reaction; in Euglena it is 
usually a decrease that causes the reaction, though when the 
light is very strong an increase may have the same effect." ' 

» H. B. Torrey, The Method of Trial and the Tropism Hypothesis, in Science, Vol. 
XXVI, p. 317 (Sept. 6, igo7). 

* The Interpretation oj the Behavior of the Lower Organisms, in Science, Vol. XXVH, 
p. 705 (May I, 1908). 

^Op. cit., p. 141. Cf. S. J. Holmes, The Selection of Random Movements as a 
Factor in Phototaxis, in the Jour, of Comp. Neurology and Psychology, Vol. XV, 
pp. Q8-112 (1905). 



Tropisms 99 

I have no space to discuss this subject further here, and 
it would be worse than foolish to express an opinion as to 
this controverted point which can be settled only by means 
of further experimenting. I will only repeat the statement 
that the weight of opinion now seems to be that the direction 
of the light does not in itself affect the activity of the organ- 
ism, but that it may influence the orienting of the organism 
when it determines the intensity of the illumination of the 
different parts of the body so that if the organism is symmet- 
rical, or if the anterior, oral end of the body is more sensi- 
tive than the posterior end, the organism becomes oriented 
towards or away from the source of Hght. I shall touch 
briefly again upon this subject when the tropism theory in 
general is discussed, but we shall now have to turn our 
attention to certain other aspects of the reactions of the 
lower organisms to light. 

The first question we must take up, and it is indeed the 
most important one in the whole subject, is as to how light 
is able to affect so greatly the movements of organisms. 
The light rays, which, according to the most recent theory 
in physics, are wave movements in the ether, are imping- 
ing upon the surface of the organism and are apparently 
causing certain changes therein. These changes may be 
of two sorts. They may be chemical changes in the body- 
surface of the organism which in turn affect the movements 
of the organism. Or they may be purely mechanical 
changes, in the sense that they push or pull muscles, loco- 
motor organs, or other parts of the body in such a fashion 
as to affect the movements of the organism. The most 
popular theory seems to be that these changes are chemical. 
This sounds plausible, to say the least, in the case of the 



100 The Science of Human Behavior 

reactions of plants to light. It has already been noted that 
the heliotropic reactions of plants are in all probabihty 
caused by unequal growth in different parts of the plant. 
If this is the case, the hght is affecting the metaboUc pro- 
cess, and this process is a chemical one. Davenport is very 
certain that the effect of hght on organisms is a chemical 
one. He speaks first of its effect on protoplasm in general. 
^'The reactions produced by light upon protoplasm are 
undoubtedly of a chemical character, and, indeed, ex- 
periments with nonhving organic compounds show that 
it has an important effect in synthesis, in analysis, in sub- 
stitution, in the production of isomeric or polymeric condi- 
tions, and in fermentation." ^ Later he speaks of its effect 
upon the movements of organisms. ''We thus see that 
organisms respond to light, and that this response, exhibited 
in movements, is not of a widely different order from the 
disturbances produced in metabolism, which in turn are of 
the same order as the chemical changes produced by Hght 
in our laboratories upon nonliving substances. In a word, 
response to light is the result of chemical changes in the 
protoplasm wrought by Hght." ^ 

Loeb also insists over and over again that Hght affects 
the movements of organisms by causing chemical changes 
in the body surface of the organism. For example, in 
trying to account for the heHotropic curvatures of plants, 
he speaks as follows : ''Let us suppose that light strikes 
a plant on one side only, or more strongly on one side than 
on the opposite side, and that it be absorbed in the super- 
ficial layers of tissue of that side. In this case we assume 
that on that side certain chemical reactions occur with 

* Experimental Morphology, New York, 1897, Vol. I, p. 210. « Op. cit., p. 211. 



Tropisms 101 

greater velocity than on the opposite side. What these 
reactions are is unknown; we may think provisionally 
of oxidations. This change in the velocity of chemical 
reactions either produces a tendency of the soft elements 
on that side to contract a Httle more than on the opposite 
side, or creates otherwise a greater resistance to those forces 
which have a tendency to elongate or stretch the plant, e.g., 
hydrostatic pressure inside the cells, or imbibition of 
certain tissue elements. The outcome will be that one side 
of the stem will be stretched more than the opposite side, 
and this will bring about a curvature of the stem." ^ So 
far he has been speaking of the positively heliotropic parts 
of plants. Later he speaks as follows of the negatively 
heliotropic parts: ''The same reasoning applies also to 
negatively heliotropic organs, e.g., roots, with the difference 
only, that in the latter case the photochemical effects result 
in a relaxation or a decreased resistance to the stretching 
forces on that side of the organ where the Hght strikes." ^ 
According to Loeb, then, Hght causes certain chemical 
changes which lead to certain mechanical results in the way 
of contractions and relaxations which influence the move- 
ments of organisms. It should be noted that he states 
that the exact nature of these chemical reactions is not yet 
known, and it is well to reserve judgment as to the causes 
of these phototropic movements in plants until more is 
known about them. 

When we come to the study of the reactions of animals 
to light, it seems less probable that the changes caused by 
light are always chemical. Loeb seems to be certain that 
they are always chemical, as indicated in the following 

* The Dynamics of Living Matter, New York, 1906, p. 118. 2 Qp^ ^it., p. 119. 



102 The Science of Human Behavior 

passage: ''First, heliotropic animals as well as helio- 
tropic plants must contain a substance on their surfaces 
which undergoes a chemical change when subjected to the 
influence of the Hght, and this change must be able to pro- 
duce changes of tension in the contractile tissue. Second, 
hehotropic animals as well as hehotropic plants possess sym- 
metry of form and a corresponding distribution of the irrita- 
bihties. These two groups of conditions determine the helio- 
tropic reaction unequivocally." ^ But it may be that in some 
cases the reaction is entirely mechanical. For example, in 
the case of these microorganisms which propel themselves by 
means of cilia or a flagellum, it may be that the light waves, 
without causing any chemical change in these locomotor 
organs, stimulate them to greater activity by pushing them. 
The Ught would in such cases act Hke a molar force. 

Chromotropism 
The reactions of organisms to color, which are usually 
called chromotropism, are of importance in this connection. 
The color sensations are caused by the differences in the 
length of the Hght waves. It is to be expected, therefore, 
that the different colors would act differently upon organ- 
isms, chemically and perhaps mechanically also. In the 
following passage, Davenport indicates some of the chemical 
effects of the different colors: "Upon metaboHsm we can 
distinguish an effect of the red rays, which are greatly 
absorbed by chlorophyll and are chiefly active in assimi- 
lation, and an effect of the blue rays, which seem to produce 
important chemical changes, increasing the production of 
carbon dioxide in plants, creating an electric current in the 

1 Comparative Physiology of the Brain and Comparative Psychology, New York, 
1900, p. 183. 



Tropisms 103 

retina as it falls thereon, and bleaching visual purple." ^ 
Loeb describes some of these chemical effects more fully : 
"We do not yet know with the same degree of certainty, 
as in the case of the process of assimilation, the relative 
hehotropic efficiency of each part of the spectrum; but 
from experiments with colored screens it appears that the 
more refractive green, blue, and violet rays of the spectrum 
are more effective hehotropically than the less refractive 
red and yellow rays. There exists thus apparently a divi- 
sion of labor, the longer light waves accelerating assimila- 
tion, the shorter waves accelerating heliotropism. This 
can be demonstrated with the aid of screens, inasmuch as 
behind red screens the plants assimilate well, while they do 
not bend or bend only slowly, toward the source of Hght; 
while behind a blue screen they bend actively toward the 
light, their assimilation being diminished." ^ Later on he 
shows in the case of certain animals that the same holds true 
for animals. "It can also easily be shown that in these 
animals, just as in plants, the more refrangible blue rays 
are more effective than the red rays, and that the latter 
act like weak Hght." ^ It appears, then, that the refrangi- 
bility of the rays of light has an effect upon the chemical 
and perhaps also upon the mechanical reactions to Hght. 
Further investigation of chromotropism will therefore un- 
doubtedly throw Hght upon the general subject of the re- 
actions of organisms to Hght.* 

1 Experimental Morphology, New York, 1897, Vol. I, p. 211. 

2 The Dynamics of Living Matter, New York, 1906, pp. 11 7-1 18. 
'Op. cit., p. 127. 

* Professor G. H. Parker has been engaged for several years in working out a 
method for producing colored light of good quality and measured intensity, with 
which to test the reactions of organisms to color. He has not yet, at the time 
of this writing, published the restdts of his investigation. 



104 The Science of Human Behavior 

For each species there is a certain optimal intensity of 
light which is most favorable to it. Jennings has defined 
the ^'optimum" and suggested how organisms reach it in 
the following passage: *'The organism generally reacts 
by a change in its behavior when the change is of such a 
nature as to lead away from the optimum. By optimum we 
mean here the conditions most favorable to the Hfe processes 
of the organism in question. Changes leading toward this 
optimum produce in many animals no reaction ; the organ- 
isms simply continue the activity which has brought about 
this change. Changes leading away from the optimum 
produce a negative reaction, by which the organism is 
removed from the operation of this change." ^ An inten- 
sity of light much above or much below the optimum is 
injurious to the organism. Each species has its own means 
for getting away from the intensity which is injurious to 
it and for reaching the optimum. I do not, however, 
mean to imply by this that the organism consciously seeks 
its optimum, for these organisms are too simple to be con- 
scious of a need for the optimum. But those organisms 
which do not react negatively to the Hght conditions which 
are injurious to it would tend to be eliminated, so that the 
species which survive tend to be those which react adap- 
tively to Hght. Thus each species has its own means for 
reaching the optimal intensity, plants by bending the stalk, 
animals by contraction or relaxation of muscles, by move- 
ments of ciHa or flagella, etc. Not all species, however, 
react so readily to Hght. For example, most colorless in- 
fusoria do not react to light of ordinary intensity.^ It is, 
however, hardly conceivable that there is any species which 

' Op. cit., p. 295. 'Jennings, op. cit., p. 128. 



Tropisms 105 

would not react under any light conditions. There is 
probably no species which would not react to extreme light, 
while the same is likely to be true for extreme absence of 
light. Extreme Hght would certainly have a destructive 
effect upon the tissues of the body, while extreme darkness 
would probably interfere with the metaboHc processes. 

Nothing has been said about vision in this discussion of 
the reactions of these microorganisms to light. Some of 
these organisms have pigment spots which may be rudi- 
mentary eyes. Experiments have been made to determine 
whether these spots play a part in determining the re- 
actions of these organisms to light. It appears that they 
do in some organisms, but apparently not in the case of 
others. This subject is of most importance in connection 
with the origin and evolution of the visual sense, so that I 
shall discuss it briefly in the chapters on the nervous system. 

Utility of Reactions to Light 

The last topic we have to discuss under the head of the 
reactions of these microorganisms to Hght is the functional 
value of these reactions. It has already been indicated 
that these reactions are subjected to a process of natural 
selection so that only those species tend to survive whose 
reactions to light favor the life processes. I will now give 
a few illustrations of the functional value of these adaptive 
reactions. 

One of the annelids, the earthworm, is negatively pho- 
to tropic, so that it burrows in the ground during the day 
and comes out only at night to feed and to have sexual in- 
tercourse. This form of reaction to light seems to be ad- 
vantageous, for if it came out during the day it would be 



106 The Science of Human Behavior 

likely to be eaten by birds.^ In similar fashion the fresh- 
water planarian is negatively phototropic, so that it stays 
under stones during the day and comes out only at night 
to feed. This form of reaction to Hght seems to be advan- 
tageous, for if it came out during the day it might be eaten 
by its enemies. 

The larvae of Porthesia chrysorrhcea^ which are the young 
caterpillars of a certain kind of butterfly, come out of their 
eggs in the nest on a tree or shrub and climb up to the tops 
of the branches and twigs because they are positively photo- 
tropic. Thus they are able to feed on the tender tips of the 
twigs and upon the buds and leaves. After they have 
eaten sufficiently they become negatively phototropic and 
crawl down again. The character of the phototropism is 
changed by the changes in the chemical composition of 
the skin of the animal caused by the metabolic process. 
This is one of the numerous cases in which changes in the 
organism caused by the internal processes or induced by 
external forces cause changes in the form of the reaction 
of the organism to Hght. 

In the case of certain winged ants both the male and 
female ants become positively phototropic at sexual matur- 
ity, which causes them to take the '* nuptial flight," during 
which they pair in the air.^ 

Reactions to light are not always, however, advantageous. 
They may be indifferent, or may sometimes be positively 
injurious. For example, certain night-flying insects are 

^ This and several of the following cases are described in T. H. Morgan, Evolution 
and Adaptation, New York, 1903, chap. XI. 

*J. Loeb, Comparative Physiology of the Brain and Comparative Psychology, 
New York, 1900, pp. 18S-190. 

'J. Loeb, Studies in General Physiology, Chicago, 1905, p. 52. 



Tropisms 107 

phototropic. Whether or not this phototropism is ever 
advantageous to them, is hard to determine. But sometimes 
it is very injurious, as when the moth flies into the flame of 
a lamp or any other source of light because it is moving 
too rapidly to turn aside. However, as has been suggested 
above, no species can long survive with reactions to Hght 
which are fatally disadvantageous to it, so that most species 
are characterized by reactions which have an adaptive 
value. 

The form of the reaction of a species to light may vary 
greatly, and such variations sometimes have great adaptive 
value. I have already suggested how the metabolic pro- 
cess may cause such variations. Various other causes might 
be mentioned, such as the period of life of the organism, 
continued exposure to Hght, which may modify the response 
to light, the temperature, the concentration of the medium, 
the chemical condition of the medium, etc.^ 

Geotropism 

One of the forces to which organisms are being constantly 
subjected is that of gravity. The reaction to gravity is 
usually called geotropism, sometimes geotaxis. If the 
reaction is towards the earth, it is positive ; if it is away from 
the earth, it is negative. Gravity seems to have most in- 
fluence upon the growth of sessile organisms, because they 
are subjected most uniformly to its power. In the case of 
plants, for example, the roots grow downward because they 
are positively geotropic, while the stems grow upward be- 
cause they are negatively geotropic. The causes of posi- 

1 Cf. C. B. Davenport, Experimental Morphology, New York, 1897, Vol. I, pp. 
196-201. 



108 The Science of Human Behavior 

live geotropism seem more evident than those of negative 
geotropism. We do not need to go into a discussion of the 
question as to what is the nature of the force of gravity, but 
we know that it pulls matter towards the center of the 
earth. Consequently it does not appear surprising that 
organisms should be pulled downward. There has been 
a good deal of discussion as to how this takes place. ^ 
Certain experiments seem to indicate that in cells whose 
contents are somewhat segregated from each other the 
heavier particles sink to the bottom. This seems to ex- 
plain the positive geotropism of certain parts of sessile 
organisms, and, as we shall see, it may also explain the 
geotropic orientation of free-moving organisms. 

But the causes of negative geotropism are much more 
obscure. It has been suggested that it is caused by the 
centrifugal force of the rotating earth.^ Certain experi- 
ments made by revolving organisms on a khnostat, a 
machine for testing the effect of the centrifugal force, 
indicate that this may explain negative geotropism in plants, 
though this is not certain. But it is doubtful if this can 
explain negative geotropism in free-moving organisms. 
In the case of many of these organisms it is evident that 
distinct orientation with respect to the line of gravity takes 
place. Various explanations have been suggested for both 
positive and negative geotropism in these cases. It has 
been suggested that it is due to the difference in pressure 
between the upper and the lower portions of the organism. 
Or it may be due to the fact that the different parts of the 
organism vary in their specific gravity so that the organism 

1 Loeb, The Dynamics of Living Matter, pp. 147-1S2 ; Davenport, Experimental 
Morphology, pp. 11 2-1 14. 

' Loeb, Studies in General Physiology, p. 182 ; Davenport, op. cit., pp. 11 2-1 13. 



Tropisms 109 

is oriented with its anterior end towards or away from the 
center of the earth. But the whole subject is so uncertain 
that it would hardly be worth while to discuss it further 
here. 

In the higher organisms orientation to gravity seems to 
take place by means of certain mineral particles called 
otohths in the auditory mechanism. 

The reaction to gravity is not as strong in many cases 
as the reactions to other forces, so that it is frequently 
annulled by one or more of these other reactions. This, 
indeed, may happen to any of these reactions. An organ- 
ism is almost always exposed to more than one of these 
forces, so that these forces are continually neutralizing and 
modif3dng each other. Consequently the behavior of an 
animal is the resultant of these forces and the responses 
of the organism to them. The geo tropic response of an 
organism may change as a result of changes in its external 
circumstances or in its physiological state. The geo tropic 
reactions seem to have functional value in many cases. 

Chemotropism 

We will now turn to the reactions of organisms to chemi- 
cal substances. By chemical substance is meant a sub- 
stance which is diffusing itself in the surrounding medium ; 
namely, the water or the air. Organisms are frequently 
oriented when they come near to these substances. Loeb 
explains such orientation as follows: ''Theoretically we 
may assume that if substances diffuse in air or in water, 
the particles move in a straight line away from the center 
of diffusion. If they strike an organism whose surface is 
affected by the diffusing substances on one side only, the 



110 



The Science of Human Behavior 




contractile protoplasm, or the muscles, turning the tip or 
the head or the whole organism toward that side, are 
thrown into a different state of contraction from their 

antagonists. The consequence 
i? a turning or bending of the 
tip or the head until sym- 
metrical points of the chemi- 
cally sensitive surface of the 
Fig. 2.— Positive chemotropisra. body are struck by the lines 

Slide showing the positive reaction r j«rr • / .i j-rc • 

of paramecia to a drop of a weak ^^ dlffuSlOn (or the dlffusmg 

solution of carbon dioxide. (After particles) at the samc angle. 

Holmes.) 

As soon as this occurs, the con- 
tractile elements on both sides of the organ, or organism, 
are in an equal state of contraction, and the animal will 
bend or move in the direction of the Hnes of diffusion." ^ 
He goes on to show that chemotropic orientation is not as 
definite usually as pho- 
totropic or geotropic 
orientation because the 
lines of diffusion are 
constantly being dis- 
turbed by variations in 
the temperature of the 
surrounding medium so 
that the Hnes of force 
are not regular. 

Jennings ^ explains the reaction of these lower organisms 
to chemical substances by means of the ** avoiding reaction." 
That is to say, when an organism comes to a region in which 

* The Dynamics of Living Matter, pp. 152-153. See also Comparative Physiology 
of the Brain and Comparative Psychology, pp. 186-187. 
« Op. cil., p. 62. 




Fig. 3. — Negative chemotropism. Slide of para- 
mecia four minutes after the introduction of a 
drop of i per cent NaCl. The drop remains 
empty. (After Jennings.) 



Tropisms 111 

is dififusing a chemical substance towards which the or- 
ganism is negatively chemotropic, it will give the avoiding 
reaction which will turn it in another direction. If the 
organism is positively chemotropic towards this substance, 
it will not react when entering the region of diffusion, but it 
will give the avoiding reaction when it comes to the bound- 
ary of the region, so that it will be held in this region. The 
degree of concentration of a solution which will produce a 
reaction varies greatly for different individuals, and also 
varies for the same individual as its sensitiveness changes. 
Chemotropic reactions frequently have great functional 
value, especially for finding food and for mating. This is 
true, for example, of the insects. These reactions aid them 
in coming in contact with their food, in depositing their 
eggs upon matter which will serve as food for the young, 
and in bringing the sexes together for purposes of pair- 
ing.^ They have a similar utihty for many other of the 
lower organisms. This chemical sense, as it is sometimes 
called, is the rudimentary form out of which differentiate 
the senses of smell and of taste. Very frequently the lower 
organisms locate their food by means of a chemical reaction. 
They are attracted to each other in similar fashion, and this 
frequently leads to conjugation, so that the reproductive 
process is stimulated. This tendency on the part of some 
of these organisms to come together has sometimes been 
called ^'sociabiHty," but it is not, of course, the sociabil- 
ity displayed by the higher organisms. Jennings ^ has 
described how paramecia tend to congregate together. 
Paramecium gives off carbon dioxide. If several of theni 

^ Cf . Loeb, The Dynamics of Living Matter, New York, 1906, p. 155. 
* Op. cit., p. 68. 



112 The Science of Human Behavior 

chance to come together, a bubble of carbon dioxide may be 
formed. Each individual gives the avoiding reaction on 
coming to the edge of the bubble, so that the paramecia 
are held in the bubble. Other individuals on entering the 
bubble are prevented from leaving in similar fashion, so that 
in course of time the group may become very large. 

Galvanotropism 

The electric current causes certain reactions in the lower 
organisms which are usually grouped under the name of 
galvanotropism or electrotropism. Loeb explains galvan- 
otropism as he does phototropism and geotropism. ''When 
parallel current curves strike a symmetrical organ or 
organism sidewise, the contractile elements, e.g. muscles, 
on one side of the organ, or organism, undergo a higher 
degree of tension than on the other side ; the outcome is a 
bending or turning of the organ or animal imtil its axis, or 
plane of symmetry, is in the direction of the current curves. 
As soon as this occurs, the symmetrical elements of the 
surface of the body are struck at the same angle by the 
current curves, and the kind and acceleration of chemical 
reaction is the same on both sides of the organism ; conse- 
quently the symmetrical muscle elements show the same 
state of contraction. But the fact that the current curves 
penetrate throughout the whole animal causes often com- 
plications which prevent an ideal orientation such as we 
observe in the case of light.'^^ The electric current 
frequently does injury to these organisms. This is prob- 
ably due to the fact that they are rarely ever subjected to 
it in nature, so that they have not become adapted to it. 

* The Dynamics of Living Matter, p. 141. 



Tropisms 



113 




Stereotropism 

Another group of reactions is that of reactions to contact. 
These are sometimes grouped under the term stereotropism 
and also under the term thigmotropism. Verworn consid- 
ers thigmotropism, or thigmo taxis as he calls it, as a form 
of harotaxis, under which term he groups 
all reactions which result from changes in 
pressure relations. "All mechanical stim- 
ulation of living substance consists in a 
change of the pressure relations under 
which it exists. Every degree of pressure 
can act as a stimulus, from crushing or 
cutting, which destroys the continuity of 
the substance, down to the slightest touch 
and the most delicate change in the pres- 
sure of the air or the water that surrounds 
the organism.'' ^ Under thigmo taxis he 
groups all reactions which result from the 
contact of living substance with bodies 
which are more solid than it. 

Davenport regards thigmotaxis, or contact irritabiHty, as 
it is perhaps more appropriately called by some writers, as 
the effect of molar agents acting upon organisms. He 
explains the effect of contact upon organisms as follows : 
*'In many non-Kving substances, especially organic com- 
pounds, violent chemical changes (explosions) are brought 
about by contact and especially by repeated vibrations. 
So, too, in protoplasm, chemical change, exhibiting itself 
in modified metabolism, frequently follows contact. The 



Fig. 4. — Stereotro- 
pism, or contact 
irritability. Par- 
amecium at rest 
against a cotton 
fiber, showing the 
motionless cilia in 
contact with the 
fiber. (After Jen- 
nings.) 



* General Physiology, London, 1899, p. 440. 



114 The Science of Human Behavior 

explanation adapted to the non-living series of phenomena 
is adapted to the Hving series also, — the molecules of the 
substance are complex, loosely associated, very unstable, so 
that even a slight mechanical disturbance will serve to 
dissociate their atoms." ^ It appears from this passage 
that contact causes a chemical change in the organism. 
The term contact irritability therefore seems to be the 
best one to apply to these reactions. In any case there 
certainly is no tropism involved in these reactions, for there 
are no Knes of force which cause them in the organisms. 
It is therefore misleading to group these reactions under 
such a name as stereotropism or thigmo tropism. 

The functional value of contact irritabihty is similar to 
that of chemotropism, because it aids greatly in securing 
food and in causing reproduction. In many cases after 
chemotropism has brought the organism to food, it is con- 
tact irritabihty which leads it to grasp it and to ingest it. 
After chemotropism has brought two individuals close to- 
gether, it usually is contact irritabihty which forces them to 
conjugate. This is also true of the higher organisms, for 
contact irritability seems to play a part very frequently, 
perhaps always, in bringing about copulation. 

Rheotropism 

Another form of reaction is reaction to a current of water, 
sometimes called rheotropism or rheotaxis. Inasmuch as 
this is a reaction to a pressure stimulus, Verwom calls this 
a form of barotaxis.^ Davenport regards it as a form 
of thigmotropism. ^*We now turn to the consideration of 
Rheotaxis, which may be regarded provisionally as a form 

1 Op. cit., p. 109. ' Op. cit., p. 444. 



Tropisms 115 

of thigmotaxis, although the possibility of its being rather 
a case of chemo taxis is not to be excluded.'' ^ He does 
not indicate why rheotropism may be a form of chemotro- 
pism. Jennings also speaks of rheotropism as if it was 
a form of stereotropism. "The reaction is essentially a 
response to a mechanical disturbance, comparable to that 
due to the touch of a soHd body." ^ 

Rheotropism is manifested frequently by higher organ- 
isms, such as fishes which tend to head upstream. But it 
has been questioned whether there is any tropism involved 
in this reaction, and the investigations of Lyon seem to 
indicate that it is simply an optical reflex and that it is an 
effort upon the part of the organism to keep itself in such a 
position that it shall appear to its sense of vision that it is 
at rest.^ It may also be that rheotropism like stereotropism 
is not a real tropism for the lower organism as well, for 
there are no lines of force acting upon the organism. The 
current of water is simply a molar agent pressing upon the 
organism. 

Rheotropism probably has functional value in a good 
many cases, though this subject has not been investigated 
very much as yet. It appears that it plays a part in bring- 
ing about fertilization in the human species, as is indicated 
in the following passage from Verwom: "It is easy to 
assume that the human spermatozoa are rheotactic and 
find their way to the egg cell by means of this property. 
When the spermatozoa come into the uterus, they meet a 
current of mucous liquid coming toward them, since the 
cilia of the epithelium Uning the uterine cavity have a 

1 op. cit., p. io8. 2 Op. cit., p. 74. 

»E. P. Lyon, Am. Jour, of Physiology, Vol. XII, p. 149 (1904). 



116 The Science of Human Behavior 

direction of stroke toward the os, and hence produce a 
current toward the outside. That it is chemotaxis of the 
spermatozoa toward the ovum which points out the path 
to them becomes very improbable when it is remembered 
that the spermatozoa wander upward in the uterus before 
the ovum has left the ovarian folUcle." ^ It is probably use- 
ful also to fish because it leads them to go up streams, 
where they can lay their eggs in quiet and safe places.^ 

Other Tropisms 

A reaction similar to rheotropism is the reaction to a 
current of air, usually called anemotropism.^ It manifests 
itself usually in winged organisms, and practically every- 
thing which has been said about rheotropism is true also 
for anemotropism. 

The lower organisms react sometimes in certain more 
or less definite ways to heat. These reactions may be 
grouped under the term thermotropism or thermotaxis. 
They seem to be caused by differences in the intensity of 
the heat at different points on the organism, thus causing 
unequal stimulation."* 

There are a number of other kinds of reactions which 
are similar to the reactions to heat, such as hydrotropism 
or hydrotaxis,^ which are reactions caused by differences in 
moisture, and tonotropism or tonotaxis,® which are reac- 
tions to differences in the density of the surrounding medium. 
These reactions have not been investigated very much as 
yet, and there is not the space to discuss them further here. 

^ Op. cit., p. 445. * Cf. Davenport, op. cit., p. 109. 

» Cf. Washburn, op. cit., pp. 154. 188-189, 288. 

* Cf. Davenport, op. cit., p. 262; Verworn, op. cit., p. 451, 

* Cf. Davenport, op. cit., p. 66. • Cf. Davenport, op. cit., p. 8g. 



CHAPTER VII 

THE EVOLUTION OF ANIMAL BEHAVIOR 

Determination of behavior by form and past experience and by 
external stimuli, 117. — Description of the behavior of amoeba, Para- 
mecium, stentor, etc., 118. — The action system, 126. — The reflex, 
128. — The physiological state of the organism as a factor in the 
determination of behavior, 131. — The regulation of behavior, 132. 
— The development of behavior in the race, 133. — Organic selection, 
134. — The laws of animal behavior, 135. 

In the preceding chapter have been reviewed briefly the 
reactions of organisms to the external forces or stimuli 
enumerated in the classifications of Davenport and Ver- 
worn which have been cited. So far as I know, all the in- 
vestigators of animal behavior are agreed that the actions 
of organisms are determined in the last analysis and in the 
long run by external forces. That is to say, the forms of 
these organisms have been determined in the past by these 
external forces. Furthermore, their experience in the past 
has been determined by their forms and by external forces. 
So that inasmuch as the behavior of an organism at any 
moment is not determined entirely by the immediate 
stimulus, but in part by its form and by its past experience, 
the behavior as a whole can in the last analysis be traced 
back to external forces. I wish therefore to discuss next the 
part played by the forms and past experience of the organ- 
isms themselves in determining the reactions of the lower 
animals. 

117 



118 The Science of Human Behavior 

The Determination of Behavior 

There has been a good deal of difference of opinion among 
the investigators of the behavior of the lower animals as to 
the extent to which this behavior is being determined by- 
form and past experience and the extent to which it is being 
determined by the immediate stimulus. This difference of 
opinion has manifested itself to the greatest extent in the 
discussion of the tropism theory. It has, perhaps, been to a 
certain extent true that the more ardent supporters of the 
tropism theory have tended to minimize the part played by 
the organism in determining its behavior, while those who 
have opposed the theory or who have not made much use 
of it have tended to emphasize the part played by the organ- 
ism in determining its behavior. This last has been some- 
what true of Jennings, who in the numerous papers he has 
pubUshed on the subject and especially in his able work on 
the ''Behavior of the Lower Organisms," which has already 
been cited several times in previous chapters, has made a 
careful and detailed study of the causes of the behavior of 
lower organisms. I sha 1 therefore review briefly the in- 
vestigations and theories of Jennings in this field. 

Jennings devotes more than two thirds of his principal 
work to an account of investigations made by him in the 
study of the behavior of several species of protozoa and of 
the lower metazoa. The first species he studies is the 
Amoeba, which is one of the lowest organisms. The Amoeba 
is a shapeless mass of jellylike protoplasm which has 
almost no structure to determine its reactions. After de- 
scribing various experiments in which it was subjected to 
different stimuli, he sums up the results as follows: "We 



The Evolution of Animal Behavior 119 

find that the simple naked mass of protoplasm reacts to all 
classes of stimuli to which higher animals react (if we con- 
sider auditory stimulation merely a special case of mechani- 
cal stimulation). Mechanical stimuli, chemical stimuli, 
temperature differences, Hght, and electricity control the 
direction of movement, as they do in higher animals. In 



cu 




Fig. 5. — Amosba Proteus, c.v., contractile vacuole; ec, ectosarc; en., endosarc; 
nu., nucleus ; ps., pseudopodia. (From Jennings, after Leidy, slightly modified.) 

other words, Amoeba has some method of responding to all 
the chief classes of Hfe conditions which it meets." ^ He 
goes on to show that the behavior of Amoeba under any 
given conditions is not determined entirely by the immedi- 
ate stimuh, but that behavior in the past is influencing pres- 
ent action. He distinguishes three main types of behavior, 
which he calls the positive reaction, the negative or avoid- 
ing reaction, and the food reaction. An Amoeba may re- 
spond in any one of these three ways to a given stimulus. 

1 op. cit., p. 19. 



120 The Science of Human Behavior 

What determines in which way it will respond, and will it 
always respond in the same way to such a stimulus ? Jen- 
nings discusses these questions as follows: ''What decides 
whether the reaction to a given stimulus shall be positive or 
negative? This question touches the fundamental prob- 
lem of behavior. The nature of the physical or chemical 
action of an agent does not alone determine the reaction, 
for to the same agent opposite reactions may be given, 
depending on its intensity, or upon various attendant cir- 
cumstances. If we should make a chemical or physical 
classification of the agents affecting movement in Amoeba, 
this would not coincide with a classification based on the 
reactions given. But the agents which produce a negative 
reaction are in general those which injure the organism in 
one way or another, while those inducing the positive re- 
action are beneficial. Any agent which directly injures 
the animal, such as strong chemicals, heat, mechanical 
impact, produces the negative reaction. The positive re- 
action is known to be produced only by agents which are 
beneficial to the organism. It aids the animal to find soUd 
objects on which it can move, and is the chief factor in 
obtaining food. Thus the behavior of Amoeba is directly 
adaptive ; it tends to preserve the Hfe of the animal and to 
aid it in carrying on its normal activities." ^ How the 
behavior of Amoeba has become adaptive, Jennings does not 
explain at this point, but as we shall see he takes up this 
subject later on. 

The next group of organisms he studies are certain species 
of bacteria. These are the lowest organisms which have a 
definite form and special organs of locomotion. It is hard 

1 Op. cit., p. 23. 



The Evolution of Animal Behavior 121 

to determine whether they are animals or plants, though 
they are usually regarded as plants. Jennings makes a 
special study of their reactions to food. He finds that their 
reactions are determined to a large extent by the needs of 
the metaboHc process. ''A relation of great significance 
becomes evident on examining the facts; behavior under 
stimulation depends on the nature of the normal life processes, 
— especially the metabolic processes. Bacteria that re- 
quire oxygen in their metabolism collect in water contain- 
ing oxygen ; bacteria to which oxygen is useless or harmful 
avoid oxygen. Bacteria that use hydrogen sulphide in 
their metaboHsm gather in that substance. Bacteria that 
require Hght for the proper performance of their metabolic 
processes gather in Hght, while others do not." ^ He sums 
up these reactions as follows: "Behavior that results in 
interference with the normal metaboHc processes is changed, 
the movement being reversed, while behavior that does not 
result in interference or that favors the metaboHc processes 
is continued." ^ Thus we see that the behavior of bacteria 
also is adaptive and regulatory. The negative reaction is 
used to avoid those things which are harmful, while the 
positive reaction is used to secure those things which are 
beneficial. He is, however, careful to point out that the 
adaptation is not always perfect. 

Next he studies Paramecium, a species of infusoria. 
Paramecium is a cigar-shaped, unicellular animal which 
propels itself by means of ciHa. It is not bilateraUy sym- 
metrical, but sHghtly spiral in form, because it has a broad, 
obHque groove on one side, the oral surface, called the 
oral groove, or peristome. The ciHa in the oral groove 

* op, cit., p. 39. » op. cit., p. 39. 



122 



The Science of Human Behavior 



make stronger strokes than the others so the head is con- 
stantly being turned away from the oral side. But at the 

same time the animal is 
rotating on its long axis, 
because the ciHa strike, 
not directly backward, 
but obliquely to the 
right, so that the ani- 
mal rolls over to the 
left. Consequently the 
tendency to move to- 
wards the aboral side is 
compensated and the 
animal moves forward 
in a spiral course. This 
spiral course is useful to 
it in giving the avoiding 
reaction. If it strikes 
an obstacle in its path, 
its cilia reverse their 
action and it moves 
backward a short dis- 
tance. Then as it starts 
forward again on its 
spiral course it will be 
moving in a somewhat 
different direction and 
may avoid the obstacle. 
If it should hit it again, 
however, it will repeat the avoiding reaction and will con- 
tinue to do so until it has passed the obstacle. " Paramecia 




Fig. 6. — Paramecium, viewed from the oral sur- 
face. L, left side; R, right side; an., anus; 
ec, ectosarc ; en., endosarc ; /.v., food vacuoles ; 
g., gullet ; tn., mouth ; ma., macronucleus ; mi., 
micronucleus; o.g., oral groove; p., pellicle; 
tr., trichocyst layer. The arrows show the 
direction of movement of the food vacuoles. 
(After Jennings.) 



The Evolution of Animal Behavior 123 

react to most of the different classes of stimuli which act 
upon them, in the way just described. Mechanical stimuli, 
such as solid obstacles, or disturbances in the water ; chemi- 
cals of all sorts; heat and cold; light that is sufficiently 
powerful to be injurious; electric shocks, and certain dis- 
turbances induced by gravity and by centrifugal force, all 
cause the animal to respond by the avoiding reaction, so 
that it escapes if possible from the region or condition that 
acts as a stimulus." ^ 

But, according to Jennings, Paramecium gives a positive 
reaction also. Upon a little analysis, however, this positive 
reaction seems to me to be nothing more than the nega- 
tive or avoiding reaction given in such a fashion as to 
keep the animal under a certain stimulus which usually is 
beneficial to it. For example, a Paramecium may swim into 
a region in which a chemical is dissolved to which it does 
not give the negative reaction. Upon and after entering 
this region it will make no change of movement. But when 
it comes to the boundary of this region it will give the avoid- 
ing reaction and will thus be kept within this region. Just 
why the negative reaction is given when the boundary of 
this region is reached is not explained, but it is contended 
that both the negative and the so-called positive reactions 
are usually beneficial to the organism, so that they must 
be adaptive and regulatory. ^'We may sum up the usual 
behavior of Paramecium under the various stimuli of the 
environment in the following way. The natural condition 
of the animal is movement. In constant external condi- 
tions (unless destructive) the movements are not changed, 
— that is, there is no reaction, — even though these con- 

1 op. cU., p. SI. 



124 The Science of Human Behavior 

ditions do not represent the optimum. But as its move- 
ments carry the animal from one region to another, the 
environmental conditions affecting it are of course changed, 
and some of these changes in condition act as stimuU, 
causing the animal to change its movements. If the en- 
vironmental change leads towards the optimum, there is 
no reaction, but the existing behavior is continued. To a 
change leading away from the optimum (in either a plus 
or minus direction), Paramecium responds by the 'avoiding 
reaction.' This consists essentially in a return to a previous 
position, through a backward movement, then in 'trying' 
different directions of movement till one is found which 
leads toward the optimum." ^ In this case, as in the previ- 
ous ones, he reserves the discussion of how the behavior of 
this organism became adaptive for a later part of his book. 
So far I have spoken only of cases in which there is but 
one stimulus acting upon Paramecium. But under ordinary 
conditions it is subjected to a combination of stimuH, so 
that its behavior is determined by all of these stimuli. 
Furthermore, its behavior is undoubtedly influenced by 
internal changes. It is difficult to study the physiological 
condition of so minute an animal as Paramecium, but there 
is good reason to believe that it is characterized at different 
times by physiological states which correspond to fatigue, 
hunger, acclimatization, etc. These states have, of course, 
been caused in part by past stimuli, so that here we have 
rudimentary examples of the modification of behavior 
through the past experiences of the animal. 

Further on Jennings gives fuller illustrations of such modifications 
in the case of Stenlor rosselii. This is a trumpet-shaped, unicellular 

> Op. cit., pp. 57-58. 



The Evolution of Animal Behavior 125 



animal which is usually attached by its foot to a water plant or piece 
of debris. If some carmine is added to the water around it, the changes 
in its behavior which result are summed up as follows : — 

"i. No reaction at first: the organism continues its normal 
activities for a short time. 

"2. Then a slight reaction by turning into a new position, — a 
seeming attempt to keep up the normal activ- 
ities and yet get rid of the stimulation. 

"3. If this is unsuccessful, we have next a 
slight interruption of the normal activities, in 
a momentary reversal of the ciliary current, 
tending to get rid of the source of stimulation. 

"4. If the stimulus still persists, the ani- 
mal breaks off its normal activity completely 
by contracting strongly — devoting itself en- 
tirely, as it were, to getting rid of the stimu- 
lation, though retaining the possibility of 
resuming its normal activity in the same 
place at any moment. 

"5. Finally, if all these reactions remain 
ineffective, the animal not only gives up com- 
pletely its usual activities, but puts in opera- 
tion another set, having a much more radical 
effect in separating the animal from the stim- 
ulating agent. It abandons its tube, swims 
away, and forms another one in a situation 
where the stimulus does not work upon it." ^ 

These changes in behavior therefore take 
place while the organism is under the same stim- 
ulus, so that they must be caused by changes in 
the organism itself. The organism appears to be "trying" different 
methods of getting rid of a stimulus which is obnoxious to it. Con- 
sequently its behavior in this respect is singularly like that of higher 
organisms, and the similarities and differences between the behavior 
of the unicellular and the higher organisms are indicated in the fol- 
lowing passage: "The same individual does not always behave 
in the same way under the same external conditions, but the behavior 
depends upon the physiological condition of the animal. The reac- 

1 Op. cit., pp. 176-177. 




Fig. 7. — Stentor rceselii 
Ehr. (From Jennings, 
after Stein.) 



126 The Science of Human Behavior 

tion to any given stimulus is modified by the past experience of the 
animal, and the modifications are regulatory, not haphazard, in char- 
acter. The phenomena are thus similar to those shown in the 'learn- 
ing' of higher organisms, save that the modifications depend upon 
less complex relations and last a shorter time." ^ 

The Action System 

It must be evident that the structure of a given organism 
must limit the number and kinds of actions which that 
organism can perform. There are, in the first place, for 
each organism a number of simple movements and then 
a larger number of combinations of these simple movements. 
The whole set of these actions taken together Jennings 
calls the action system. For example, he describes the ac- 
tion system of Paramecium as follows: ''The action 
system of Paramecium is based chiefly on the spiral course, 
with its three factors of forward movement, revolution on 
the long axis, and swerving toward the aboral side. The 
behavior under most conditions is determined by variations 
in these three factors. Such variations, combined in a 
tjrpical manner, produce what we have called the avoiding 
reaction." ^ 

Among the higher organisms we do not expect to find an 
animal without wings flying nor an animal without feet 
walking. So among the lower organisms behavior is Hmited 
and determined to a large extent by structure. For ex- 
ample, the infusoria can be divided according to their be- 
havior, which is determined in large part by structure, 
into those that are sessile, those that creep over surfaces, 
and those that swim freely. "The behavior is simplest 
and least varied in the free-swimming organisms; more 

> op. cit., p. 179. ' Op. cil., p. 107. 



The Evolution of Animal Behavior 127 

varied in those which habitually creep along a surface; 
most complex in those which live attached. The reason 
for this seems to be as follows : In the open water the con- 
ditions are exceedingly simple. The free-swimming organ- 
ism may escape an injurious stimulus simply by swimming 
away. In the fixed organism, on the other hand, the con- 
ditions are more complex. At any moment both the solid 
and the free liquid are acting on the organism. For a 
fixed animal to obtain food and escape injurious conditions, 
varied devices are necessary. It cannot- at once solve any 
difficulty by departing, as the free organism can. We find, 
then, that such fixed organisms have developed varied re- 
action methods." ^ We have already illustrated these 
differences in the case of a free-swimming organism like 
Paramecium, whose reactions are very simple, and of an 
organism Hke Stentor rcBselii, which is sessile most of the 
time, but creeps over surfaces sometimes, and whose re- 
actions are much more varied than those of Paramecium. 

Jennings next describes studies he has made in the be- 
havior of certain species of the lower metazoa. I have not 
the space to summarize these studies, though they are of the 
greatest interest. We can only note his general conclusions. 
There are two great differences between the metazoa and 
the protozoa. The metazoa are multicellular, while the 
protozoa are unicellular; the metazoa have a nervous 
system, while the protozoa do not have one. On account 
of these differences it has been thought by many that the 
differences between the behavior of the protozoa and of 
the lower metazoa must be very great. But Jennings 
comes to a different conclusion. After making a detailed 
1 op. cit., p. 1 80. 



128 The Science of Human Behavior 

comparison of the behavior of these two groups of organisms 
he expresses himself as follows: "All together, there is 
no evidence of the existence of differences of fundamental 
character between the behavior of the Protozoa and that 
of the lower Metazoa. The study of behavior lends no 
support to the view that the life activities are of an essen- 
tially different character in the Protozoa and the Metazoa. 
The behavior of the Protozoa appears to be no more and no 
less machinehke than that of the Metazoa ; similar prin- 
ciples govern both." ^ With respect to the nervous system 
he comes to the same conclusion as Loeb ; namely, that "we 
do not find in the nervous system specific qualities not found 
elsewhere in protoplasmic structures," so that most of the 
activities which have usually been considered pecuHar to 
the nervous system can be demonstrated in the protozoa, 
in which there is no nervous system. This is a subject 
which will be discussed in the next chapter on the nervous 
system. 

Several times in the course of this exposition of Jennings* 
work it has been stated that he explains in the latter part 
of his book how the behavior of these lower organisms be- 
comes adaptive and regulatory. I will now summarize 
this explanation and his general theory as to the behavior 
of the lower organisms. 

The Reflex 

He commences with a discussion of the nature of reflex 
action. By reflex action is frequently meant the contrac- 
tion of a muscle when a certain nerve is stimulated. It is 
called reflex because the stimulation is supposed to pass 

* op. cit., p. 263. 



The Evolution of Animal Behavior 129 

along the sensory nerve to the central nervous system and 
is then reflected back to a muscle. It is evident that for 
this sort of reflex action a nervous system is needed, and 
this kind of reflex action will be discussed in the next chap- 
ter. But the term reflex action is sometimes appHed to 
any case of an invariable reaction to a given stimulus. In 
this sense it is simply a type of action without regard to the 
existence of a nervous system, and it is in this sense that 
Jennings uses the term. It is beHeved by some that the 
reactions of the lower organisms are reflex in this sense, that 
they are all invariable. But Jennings denies this on the 
ground that the same stimulus will not necessarily produce 
the same reaction invariably, because changes in the phys- 
iological state of the organism may cause variations in 
the reaction. ''If, then, we consider the reflex an invari- 
able reaction to a given stimulus, we cannot hold that be- 
havior in lower organisms is made up of reflexes. Indeed, 
the fact that stands out most clearly in the behavior is the 
following: Each stimulus causes as a rule not merely a 
single definite action that may be called a reflex, but a 
series of 'trial' movements, of the most diverse character, 
and including at times practically all the movements of 
which the animal is capable. The reaction to a given 
stimulus depends on the physiological state of the organ- 
ism, not alone on its anatomical structure; and physio- 
logical states are variable. This is true both for the 
infusoria and for man." ^ 

This tendency to characterize the behavior of the lower 
organisms as purely reflex arises out of the desire to explain 
this behavior on mechanical grounds without assuming 

1 op. cit., p. 280. ] 



130 The Science of Human Behavior 

the existence of consciousness. This is, I believe, a laud- 
able desire. But just because the behavior is not invari- 
able, we do not have to assume that consciousness exists 
and that therefore the behavior is not purely mechanical. 
The physiological state of the organism may be regarded 
as a part of its mechanical structure, so that when we ex- 
plain variations in its behavior by changes in its phys- 
iological state, we are still explaining its behavior on 
mechanical grounds. But the behavior of higher or- 
ganisms also can be explained in similar fashion on mechani- 
cal grounds, so that no distinction in this respect can be 
made between the behavior of the higher and the lower 
organisms. If, then, we are to regard reflex action as in- 
variable reaction to a given stimulus, no species is charac- 
terized with reflex action. We may, however, give a 
different meaning to the term and mean simply that the 
behavior of an organism is determined by its physical and 
chemical characteristics. It is evident that in this sense 
the behavior of every species of organism is reflex, and con- 
sequently no distinction can be made between the higher 
and the lower species. ''What a given organism does 
under stimulation is limited by its action system, and 
within these limits is determined largely by its physiological 
condition at the time stimulation occurs. In the lowest 
organism the action system confines the variations in be- 
havior within rather narrow limits, and the different phys- 
iological conditions distinguishable are few in number; 
hence the behavior is less varied than in higher animals. 
But the difference is one of degree, not of kind." ^ 

» op. cil., p. 281. 



The Evolution of Animal Behavior 131 

The Physiological State 

Since we must take the physiological state into consid- 
eration in studying the behavior of an organism, we must 
consider what determines the physiological state. In the 
first place, the physiological state of an organism may be 
changed by progressive internal processes, especially those 
of metabolism. These changes are governed by the laws 
of metaboHsm. In the second place, the physiological state 
of an organism may be changed by the action of external 
forces. From the study of these changes, Jennings deduces 
what he calls the law of the resolution of physiological states, 
which he regards of the greatest importance in explaining 
the behavior of organisms. He states this law as follows : 
^^The resolution of one physiological state into another he- 
comes easier and more rapid after it has taken place a number 
of times. ^^ ^ This law is based upon the fact that a phys- 
iological state is a dynamic condition, not a static one. 
"It is a certain way in which bodily processes are taking 
place, and tends directly to the production of some change. 
— The changes toward which the physiological state tends 
are of two kinds. First, the physiological state (like the 
idea) tends to produce movement. This movement often 
results in such a change of conditions as destroys the phys- 
iological state under consideration. But in case it does 
not, then the second tendency of the physiological state 
shows itself. It tends to resolve itself into another and 
different state. Condition i passes to condition 2, and 
this again to condition 3. This tendency shows itself 
even when the external conditions remain uniform."^ 

1 op. cit., p. 291. 2 Op. cit., p. 289. 



132 The Science of Human Behavior 

The law which has been cited is based upon this second 
tendency and indicates that the resolution of one physio- 
logical state into another takes place more readily the more 
frequently it is repeated. Sometimes where a number of 
states follow each other in a series, the resolution of one into 
the other may come to take place so rapidly as to be in- 
stantaneous, so that only the last state determines what the 
form of behavior is to be. Jennings believes that this law 
explains in large part what are called memory, association, 
habit formation, and learning in the higher organisms. But 
he beheves that it applies to the lower organisms as well, and 
that the only differences between organisms is as to the 
readiness with which the quick resolution of one physiologi- 
cal state into another becomes established and the extent 
to which such a habit is permanent. A Httle further on he 
shows that the adaptive and regulatory character of be- 
havior grows in large part out of the working of this law. 

He then classifies the factors upon which behavior de- 
pends under the following heads : — 

"i. The present external stimulus. 

"2. Former stimuU. 

"3. Former reactions of the organism. 

"4. Progressive internal changes (due to metabolic pro- 
cesses, etc.). 

''5. The laws of the resolution of physiological states 
one into another." ^ 

He now states a principle which he says is of the greatest 
importance for the understanding of behavior. It would 
seem as if this principle should have been introduced much 
earlier in the book, for it throws Hght on the "method of 

^ Op. cii., p. 292. 



The Evolution of Animal Behavior 133 

trial " which he has already discussed. This is the principle 
which has sometimes been called the "selection of over- 
produced movements, " but which Jennings prefers to call 
the "selection of the proper conditions of the environment 
through varied movements.'^ He describes the phenomena 
from which this principle is deduced as follows: "The 
stimulus does not produce directly a single simple move- 
ment (a reflex act) of a character that relieves the organism 
at once from the stimulating condition. On the contrary, 
stimulation is followed by many and varied movements, 
from which the successful motion is selected by the fact 
that it is successful in causing cessation of stimulation." ^ 

Development of Behavior 

He devotes one chapter to the discussion of the develop- 
ment of behavior in the individual and in the race. Enough 
has been said to illustrate the development of behavior in 
the individual, but a word should be said about its develop- 
ment in the race. Jennings believes that in unicellular 
species forms of behavior acquired by individuals may be 
transmitted directly to their offspring, because in these 
species there is no distinction between germ cells and body 
cells, so that all acquired characters belong to the germ cells. 
But the situation is very different in multicellular organisms, 
for in them acquired characters are rarely if ever transmitted 
from parents to offspring. Consequently, if forms of be- 
havior are to become racial as well as individual, it must be 
through some other means. Jennings believes that the 
development of racial forms of behavior has come about 
through the natural selection of congenital variations and 

* op. cit., p. 302. 



134 The Science of Human Behavior 

especially through that form of natural selection which 
has been called organic selection by J. Mark Baldwin, Lloyd 
Morgan, and H. F. Osborn. The theory of organic selec- 
tion ^ was formulated in reply to certain criticisms of the 
theory of natural selection. It was contended that the 
theory of natural selection did not provide for a series of 
variations along a definite line of evolution, because the 
variations appear purely by chance, and the selection of 
them also is purely by chance. According to the theory 
of organic selection, the selection of these chance variations 
is guided and determined in part by characters acquired 
by individuals. That is to say, variations will appear by 
chance which are beneficial to the individual, but which are 
not sufficiently great to be decisive in the struggle for ex- 
istence. These variations are shielded and conserved by 
individual accommodations until they are sujQiciently great 
to be selected for their own sake. This theory has been 
much criticized, but Jennings apparently thinks it sound. 
As appHed to behavior, he puts it as follows: ''Thus 
individual selection and natural selection necessarily work 
to the same result. One selects from among the different 
acts of the same individual, the other from among those of 
different individuals. The thing selected is the same in each 
case, — namely, the adaptive reaction." ^ 

In the following chapter he discusses the relation of 
behavior in lower organisms to psychic behavior. Inas- 
much as psychic behavior is to be discussed in a later chap- 
ter on consciousness I shall not dwell upon the matter here, 
except to say that he points out phenomena in the behavior 

» Baldwin gives a good exposition of this theory and its history in Development 
and Evolution, New York, 1902. * Op. cit., p. 325. 



The Evolution of Animal Behavior 135 

of these lower organisms which seem to be analogous to 
such psychic characteristics as perception, discrimination, 
choice, attention, etc., in higher organisms. 

In the last chapter he points out again, as he already has 
done at the beginning of the book, that behavior illustrates 
only one form of regulation and that regulation exists in 
the other processes of the organism. *' Behavior is merely 
a collective name for the most obvious and most easily 
studied of the processes of the organism, and it is clear that 
these processes are closely connected with, and are indeed 
outgrowths from, the more recondite internal processes. 
There is no reason for supposing them to follow laws differ- 
ent from those of the other life processes, or for holding 
that regulation in behavior is of a different character from 
that found elsewhere." ^ 

This review of Jennings can be closed best by giving his 
final summary of the fundamental features of the method 
of individual regulation. *'The organism is a complex 
of many processes, of chemical change, of growth, and of 
movement; these are proceeding with a certain energy. 
These processes depend for their unimpeded course on their 
relations to each other and on the relations to the environ- 
ment which the processes themselves bring about. When 
any of these processes are blocked or disturbed, through 
a change in the relations to each other or the environment, 
the energy overflows in other directions, producing varied 
changes, — in movement, and apparently in chemical and 
growth processes. These changes of course vary the re- 
lations of the processes to each other and to the environ- 
ment; some of the conditions thus reached relieve the in- 

' op. cit., p. 339. 



136 The Science of Human Behavior 

terference which was the cause of the change. Thereupon 
the changes cease, since there is no further cause for them ; 
the reheving condition is therefore maintained. After 
repetition of this course of events, the process which leads 
to reUef is reached more directly, as a result of the law of 
the readier resolution of physiological states after repeti- 
tion. Thus are produced finally the stereotyped changes 
often resulting from stimulation. This method of regula- 
tion is clearly seen in behavior, where its operation is, in 
the later stages, what is called intelligence. Its application 
to chemical and form regulation is at present hypothetical, 
but appears possible." ^ 

In an earlier chapter it was shown how difficult it is to 
determine the relative importance of external and internal 
forces in organic evolution. It is now evident that the 
same thing is true in the study of animal behavior. This 
is illustrated in the writings of two of the investigators 
whose work has been discussed. We have seen that Loeb 
emphasizes the part played by external forces in the deter- 
mination of behavior, while Jennings emphasizes the com- 
plexity of even the lowest organisms and the consequently 
important part played by internal forces. Further research 
will throw more fight upon the relative importance of these 
two sets of forces. 

We have seen that the typical form of behavior for the 
lowest organisms without a nervous system is the tropism, 
meaning by that term any direct response of an organism 
to an external force. In the succeeding chapters wiU be 
discussed the more indirect and complex forms of behavior. 

» op. cU., pp. 34^350. 



CHAPTER VIII 

THE EVOLUTION OF THE NERVOUS SYSTEM AND THE 
REFLEX ACTION 

Progressive increase in the self-determination of behavior, 137. 

— Nerve cells and fibers, 137. — The specific qualities of nervous 
matter, 138. — Definitions of the reflex action, 140. — Receptor, 
adjustor, and effector organs, 143. — The simple reflex action, 144. 
— The conductibility of nervous matter, 145. — The adaptive char- 
acter of reflex actions, 146. — The origin of the nervous system, 147. 

— The appropriation of effectors by the nervous system, 149. — 
The selective excitability of receptor organs, 150. — The neurone, 
154. — The connections between the neurones, 155. — The central 
nervous system, 156. 

In the last three chapters have been discussed the direct 
reactions of the lower organisms to external forces. We 
found that the behavior even of these lower organisms is 
to a certain extent self-determined ; that is to say, it is 
determined in part by the structure of the organism and 
by forces which originate within the organism. Such self- 
determination of behavior increases as we go up in the or- 
ganic scale. In animals this is in large part due to the 
evolution of the nervous system, so that the peculiar fea- 
tures of the behavior of the higher animals must be attrib- 
uted principally to this fact. We must therefore trace 
the evolution of the nervous system in order to understand 
the behavior of the higher animals, and especially of man. 

Specific Qualities of Nervous Matter 

The nervous system consists of nerve cells and fibers which 
extend all over the body and which influence the behavior 

137 



138 The Science of Human Behavior 

of the organism by determining the actions of the muscles 
and glands with which they are connected. The functions 
performed by the nervous system are so peculiar to itself 
that it has been the tendency of some to draw a sharp Hne 
of distinction between the nervous system and the rest of 
the organism. But others have contended that nervous 
substance is nothing more than a somewhat speciahzed 
form of protoplasm. For example, Loeb says that *'irri- 
tabihty and conductibiHty " are the only quaHties essential 
to nervous reactions and that ''these are both common 
qualities of all protoplasm." ^ According to him, the only 
difference between ordinary protoplasm and nervous sub- 
stance is that nerves ''are quicker and more sensitive con- 
ductors than undifferentiated protoplasm." ^ 

Jennings also is inclined to take this view. After review- 
ing the similarities between the behavior of animals with 
and those without a nervous system, he speaks as follows : 
*'A comparison of the behavior of the Protozoa with that 
of the lower Metazoa lends powerful support to that view 
of the functions of the nervous system which is so ably 
maintained by Loeb in his brilliant work on 'The Com- 
parative Physiology of the Brain and Comparative Psy- 
chology.' According to this view we do not find in the 
nervous system specific qualities not found elsewhere in 
protoplasmic structures. The qualities of the nervous 
system are the general quaHties of protoplasm. Certain of 
these general quahties have become much accentuated in 
the protoplasm of the nervous system, while in the remain- 
der of the protoplasm of the metazoan body they are less 

» Comparative Physiology of the Brain and Comparative Psychology, New York, 
1900, p. 5. * Op. cit., p. 6. 



The Evolution of the Nervous System 139 

strongly marked, being partially obscured by differentia- 
tions in other directions.'' ^ 

Looking at this question from the evolutionary point of 
view, it is inconceivable that there is any absolute distinc- 
tion between the nervous system and the rest of the organ- 
ism, because we know that all parts of the organism have a 
common origin and that all of them have differentiated 
from the primordial protoplasm. It is not surprising that 
writers like Loeb and Jennings, who have been leaders in 
the investigation of the behavior of the lower organisms, 
should minimize the differences between the animals with- 
out and those with a nervous system, for they are familiar 
with the species in which the nervous system is in a very 
rudimentary state, so that the differences in behavior be- 
tween these species and those without a nervous system 
cannot be very great. But in the higher animals the nerv- 
ous system, because of its specialized powers of conducti- 
bility, integrates a complex organism in a way which would 
be utterly impossible without a nervous system. So that 
while nervous matter is in the same evolutionary order 
with the other parts of the organism, and while we may agree 
with Jennings that most if not all of the features of behavior 
in the animals with a nervous system are to be found in a 
rudimentary form in the species without a nervous system, 
yet we must bear in mind that such behavior becomes far 
more complex in the higher animals and that most of the 
psychic phenomena which characterize the higher species 
would have been impossible without a nervous system. 

It will be impossible in this chapter to give an extended 
accoimt of the evolution of the nervous system or a detailed 

1 Behavior of the Lower Organisms, New York, 1906, pp. 263-264. 



140 The Science of Human Behavior 

description of it as it now exists in the higher animals. Such 
a description is to be found in any treatise on neurology, 
and there is some literature on the evolution of the nervous 
system, though this Uterature is still somewhat Umited. 
But the more important points, which will help us to under- 
stand the behavior of the higher animals, will be discussed. 

The Reflex Action 

Most discussions of the nervous system commence with 
the reflex action. The reason for this is that many writers 
on the subject regard the reflex as the fundamental type 
or unit of nervous action. For example, McDougall says 
that the simple reflex is "the fundamental type of all nerv- 
ous action."^ Parker says that "the physiological unit 
in the operations of the nervous system is the reflex." ^ 
But as we have already noted in the last chapter, this term 
has two meanings, and we must make clear just what we 
mean by it. Most of the writers who defme reflex action 
indicate the two meanings. For example, Hobhouse speaks 
as follows of the term: "The most primitive form in 
which response is adapted to requirements is that in which 
a simple sensory stimulus calls forth a uniform reaction on 
the part of the organism. Such a response is known as 
Reflex action." But he goes on immediately to say: 
"This is an extended usage, and etymologically is, it must 
be admitted, not altogether appropriate. The term applies 
strictly to animals with a developed nervous system. In 
such animals the reflex act consists of two distinct move- 



* W. McDougall, Physiological Psychology, London, 1905, p. 15. 
2 G. H. Parker, The Origin of the Nervous System and its A ppropriation of Electors, 
in the Popular Science Monthly, Vol. LXXV (1909), p. 56. 



The Evolution of the Nervous System 141 

merits or processes, a sensory or afferent process, and a 
motor or efferent process." ^ Loeb speaks at first of a 
reflex as follows: *^A reflex is a reaction which is caused 
by an external stimulus, and which results in a coordinated 
movement."^ But a little further on he says: ''This 
passage from the stimulated part to the central nervous 
system, and back again to the peripheral muscles, is called 
a reflex. '* ^ It is evident that the first statement involves 
a broader meaning than the second one, unless he means to 
imply that a coordinated movement is impossible without 
a nervous system. 

It is evident in the case of all these writers that each one 
of them first defines reflex action as being a broad type of 
reaction which does not require a nervous system, and then 
defines it more narrowly as a type of action for which a 
nervous system is essential. It is true that nervous re- 
actions are in the same evolutionary order as reactions in 
organisms not possessing a nervous system. This probably 
explains why so many writers have assimilated the two types 
of reaction as coming under the same name. For example, 
this is what Verworn has done. First he describes a reflex 
action in general. "The essence of tho reflex action con- 
sists in the fact that an element that appreciates stimuli 
and an element that reacts to stimuli are so put into re- 
lation with one another by a central bond, that every 
stimulus acting upon the appreciating element is conducted 
first to the center, and thence, as an impulse to a reaction, 
to the reacting element. Such a mechanism, in which 
every stimulus acting upon the sensory end calls out with 

1 L. T. Hobhouse, Mini in Evolution, London, 1901, p. 28. 
2 Op. ciU, p. I. } Op. cit., p. 2. 



142 The Science of Human Behavior 

machine-like certainty a reaction at the other end, is a re- 
flex arc^ ^ Then he describes it as found in a unicellular 
organism without a nervous system. ''The most primitive 
form of a reflex arc exists in unicellular organisms, the cell 
body of which possesses both the sensory and the motor 
elements, and even functions also as the central bond for 
the two." ^ Finally he describes it as found in a multi- 
cellular animal with a nervous system. ''What in all these 
cases is differentiated within a single cell, is in the nervous 
system of animals distributed to several cells. In the 
simplest case of the latter, three different cells are con- 
cerned. One cell, the sensory cell, receives the stimulus; 
from this a centripetal nerve path conducts to a central 
cell, the ganglion cell, and from here a centrifugal nerve 
path conducts to a cell that performs the reaction, the 
motor end cell. But this form of reflex arc is realized per- 
haps only in the invertebrates. In vertebrates, so far as 
the conditions are known, a fourth cell at least is interpolated 
in the arc, since in place of one ganglion cell at least two 
are present, one of which receives the stimulus from the 
sensory cell and conducts it to the other, while the other 
transfers the impulse to the motor end cell." ^ 

In similar fashion Jennings, after considering various 
meanings which have been given to the term reflex action, 
arrives at the very broad definition of a reflex "as an in- 
variable reaction to a simple stimulus." ^ This is to be 
expected of Jennings, for, as we have already seen earlier 
in this chapter, it is his tendency, like Locb, to minimize 
the differences between the organisms without and those 

^ M. Verwom, General Physiology, London, iSgg, p. 576. 
* Op. cit., p. 577. » Op. cit., p. 278. 



The Evolution of the Nervous System 143 

with a nervous system. But, as I have contended, the 
differences between the behavior of an animal with a nerv- 
ous system and the behavior of one without a nervous 
system are so great that it is worth while to emphasize 
them. Consequently I am in favor of restricting the term 
reflex action to the reactions of animals with a nervous 
system. For doing so we have the weighty authority of 
Sherrington. He defines reflex action first as follows: 
"These reactions, in which there follows on an initiating 
reaction an end-effect reached through the mediation of 
a conductor, itself incapable either of the end-effect or, 
under natural conditions, of the inception of the reaction, 
are 'reflexes.'"^ Then he restricts the meaning of the 
term as follows: "It seems better to reserve that ex- 
pression for reactions employing specifically recognizable 
nerve processes and morphologically differentiated nerve 
ceUs." 2 

I shall therefore use the term reflex action only in the 
restricted sense of meaning the reaction of muscle or gland 
or other effector organ caused by a nervous stimulus. Let 
us see what is the mechanism of this reaction. Parker says 
that it falls into three parts. " The first of these is the sense 
organ or receptor, which, as its name impHes, receives the 
external stimulus ; the receptor is also the seat of the pro- 
duction of the nerve impulse. The second is the central 
nervous organ or, as it may be called, the adjustor, which is 
concerned with directing the impulse toward the appro- 
priate end organ and with modifying it in accordance with 
the peculiar reaction to be obtained. The third and last is 

^ Charles S. Sherrington, The Integrative Action of the Nervous System, New York, 
1906, p. 6. » Op. cit., pp. 6-7. 



144 The Science of Human Behavior 

the effector or organ brought into action by the impulse, 
such as a muscle or gland." ^ Sherrington describes the 
reflex arc as including the following: ^'An ejfector organ, 
e.g., gland cells or muscle cells; a conducting nervous path 
or conductor leading to that organ ; and an initiating organ 
or receptor whence the reaction starts." ^ It is to be noted 
that Parker includes a central nervous organ in the reflex 
mechanism, and Loeb impHes the same in a passage which 
has already been cited. The use of the word reflex also 
seems to indicate that a central nervous organ must be in- 
cluded in the reflex mechanism, for it implies that the cen- 
tral nervous system is reflecting the stimulus received from 
the sense organ upon the motor organ just as a mirror re- 
flects objects. But Sherrington does not include a central 
nervous organ, and it certainly seems unnecessary for a 
simple reflex, for which are needed only a sense organ and a 
motor organ with a conducting nervous path between them. 
It is to be noted, also, that a muscle or gland is included in 
the reflex mechanism. A muscle or gland is not a part of 
the nervous system, but it performs an essential part of a 
reflex action, — in fact, the most important part, — for it is 
the only part which is visible and which constitutes a part of 
the behavior of the animal. Therefore a muscle or gland 
must always be assumed as essential to a nervous reaction. 
A simple reflex would take place if an effector organ 
responded to a receptor organ, while the rest of the organ- 
ism remained quite indifferent to the reaction. But it is 
doubtful if a simple reflex ever takes place, for all parts of 
the nervous system are connected together so that it would 
hardly be possible for such a reaction to take place without 

1 op. cit., p. 57. ' op. cit., p. 7. 



The Evolution of the Nervous System 145 

affecting other parts of the system.^ If an organism pos- 
sessed but one receptor and but one effector, a simple reflex 
might be possible, but it is doubtful if such an organism 
exists. 

Evolution of the Nervous System 

Let us now consider in somewhat more detail the evo- 
lution of the nervous system. As has been shown, the 
characteristic of conductibility possessed by nervous matter 
is not peculiar to it, for it characterizes, only in a lesser 
degree, protoplasm in general. Stimuli are carried through 
protoplasm either by mechanical or by chemical means. 
In a multicellular organism, if the intercellular material is 
solid, stimuli are likely to be carried by mechanical 
means; if the intercellular material is fluid, stimuli are 
hkely to be carried by chemical means. But in both 
cases the conduction of the stimulus is delayed some- 
what by the passage from one cell to another. Hence 
it was that where rapidity of conduction was needed, a 
special class of cells began to develop whose special function 
it was to carry these stimuli and thus connect the different 
parts of the organism together. These cell^ are usually 
elongated and stretch out protoplasmic threads in the 
direction in which the stimuli are to travel. Sherrington 
has summed up the evolution of the nerve cells in the fol- 
lowing words: "But the internal interconnection of the 
multicellular organism is not restricted to intercellular 
material. Intercellular material is, after all, no Hving 
channel of communication, delicately responsive to living 
changes though it may be. An actual living internal bond 

1 Cf . Sherrington, op. cit., pp. 7-8. 
L 



146 The Science of Human Behavior 

is developed. When the animal body reaches some degree 
of multicellular complexity, special cells assume the ex- 
press office of connecting together other cells. Such cells, 
since their function is to stretch from one cell to another, 
are usually elongated; they form protoplasmic threads, 
and they interconnect by conducting nervous impulses. 
And we find this hving bond the one employed where, as 
said above, speed and nicety of time adjustment are re- 
quired, as in animal movements, and also where nicety of 
spatial adjustment is essential, as also in animal move- 
ments." 1 

Just how these nerve cells evolved, it would be im- 
possible to describe here in detail, but it goes without 
saying that in their case, as with all parts of the organism, 
variation and selection were the forces at work. The in- 
dividuals which responded most readily and most advan- 
tageously to the stimuli of life-or-death importance would 
be selected out for survival, so that in course of time there 
evolved this system of cells which are peculiarly sensitive 
to stimuH. Thus the nerve cells are d'st'nctly adaptive 
in their character. Loeb suggests this thought when he says 
that many reflex movements are ''purposeful" in their 
character.^ He illustrates this statement by mentioning 
several reflexes which remove the organism from harmful 
stimuH. It is, however, unfortunate that he should use 
the term ''purposeful," for this suggests that they are 
telic in their character, whereas he himself insists that there 
is no intelligence back of these reflexes necessarily, how- 
ever well planned they may appear to be. The term 
"adaptive" certainly is much more suitable. 

^ Op. cit., p. 5. '* Op. cU., p. 2. 



The Evolution of the Nervous System 147 

But while we are discussing the evolution of the nervous 
system, we must not forget the effectors, which, as we have 
seen, form a necessary part of every reflex. There have 
been various theories as to the relation of the evolution 
of the effectors to the evolution of the nervous system. 
One theory has been that the nervous system evolved be- 
fore the effectors. Another theory has been that they 
evolved at the same time. A third theory has been that 
the effectors evolved before the nervous system. In view 
of our foregoing statement that the effectors form a neces- 
sary part of every reflex, it does not seem likely that the 
nervous system would evolve before the effectors. We 
have already noted the adaptive character of the nerve 
cells. We have seen that they aid animals in the strugg^-e 
for existence by making them more sensitive to stimuli 
which are of Hfe-or-death significance. But it is evident 
that it would be of no assistance to these animals to be 
sensitive if they did not have effectors in the form of mus- 
cles which could take them away from harmful stimuli 
and propel them toward those that are beneficial. It there- 
fore seems most probable that the evolution of the effectors 
began, to say the least, before that of the nervous system, 
though later the evolution of the two could go on together. 

This is the position taken by Parker in his series of papers 
entitled "The Origin of the Nervous System and its Ap- 
propriation of Effectors." His arguments in behalf of 
this theory are very convincing. In the following words 
he shows how difficult it is to believe that receptors or 
sense organs could evolve before there were any effectors : 
"A receptor or sense organ alone would be of no service 
whatever to an animal; it would resemble a telephone 



148 The Science of Human Behavior 

receiver disconnected from the rest of the system. In a 
similar way the adjustor or central organ is useless without 
at least some other element in the reflex apparatus. The 
only mechanism sufficient in itself is the effector, which, 
if it can be brought into action by direct stimulation, may 
accompHsh something serviceable to the animal. It is 
therefore improbable that we shall find multicellular ani- 
mals that possess either receptors or adjusters without 
effectors, but it is conceivable that primitive metazoans 
may have effectors without other parts of the typical neu- 
romuscular mechanism." ^ He describes a certain species 
of sponge which possesses muscle cells in the form of sphinc- 
ters, but no nervous mechanism, so that these effectors must 
be brought into action by direct stimulation. ''Thus the 
sponge would represent the first stage in the differentiation 
of a neuromuscular mechanism, i.e., one in which the effec- 
tor in the form of a primitive muscle-cell is the only ele- 
ment present. In my opinion it is around these contractile 
cells that the nervous organs of the higher metazoans have 
developed, and I therefore believe that these effector ele- 
ments are the most primitive members in the typical neuro- 
muscular mechanism." ^ Such independent effectors may 
be found also in higher animals, as Parker indicates in the 
following passage: ''If independent effectors occur in 
sponges, it is not unlikely that they may be present in the 
higher animals, and as possible examples of these the sphinc- 
ter pupillae of the eye in vertebrates and the heart-muscle 
may be considered." ^ These are the facts that lead Par- 
ker to the conclusion that "effectors in the form of muscles 
preceded in an evolutionary sense the receptors and ad- 

1 op. cU., p. s8. « op. cit., pp. 59-60. » op. cit., p. 60. 



The Evolution of the Nervous System 149 

justors, and formed the centers around which these organs 
developed later." ^ 

Following the independent effector stage, according to Par- 
ker, comes the receptor-effector stage, and then the central 
nervous organs develop and take their places between the 
receptors and effectors. These three stages he describes 
as follows: "The first was that of the independent 
effector, the muscle which was brought into action by the 
direct influence of environmental changes as seen in the 
pore sphincters of sponges. The second stage was that of 
the combined receptor and effector in which the receptors, 
in the form of diffuse sensory epithelia or speciaKzed sense 
organs, served as dehcate triggers to set the muscles in 
action and thereby render the effectors responsive to a 
wider range of stimuli than they would be under independ- 
ent stimulation. Finally, the third stage is seen in the 
complete neuromuscular mechanism in which a central 
nervous organ or adjustor has developed between the recep- 
tors and the effectors. This adjustor serves as a switch- 
board for nervous transmission and a repository for the 
effects of nervous activities." ^ 

In his last paper, Parker discusses what he calls "the 
appropriation of effectors." He calls attention to the fact 
that in the third stage described above the nervous system 
is connected not only with muscles, but also with electric 
organs, chromatophores, glands, luminous organs, etc. 
These effectors, he thinks, are recent acquisitions by the 
nervous system. He thinks also that independently and 
newly developed muscles have been acquired by the nerv- 
ous system. I have not the space to discuss fully his argu- 

» op. cit., p. 64. 2 op. cit., p. 338. 



150 The Science of Human Behavior 

ments and the many illustrations he gives. But it appears 
from his discussion of the subject that the nervous system 
may at any time acquire control over more effectors, thus 
extending its sway over a larger part of the animal organism. 
He sums up this process in the following words: "We 
must picture to ourselves as steps in the evolution of the 
nervous system, not only the independent origin of muscle 
around which the nervous organs subsequently develop, 
but also the independent origin of other effectors such as 
chroma tophores, glands, and phosphorescent organs and 
the secondary appropriation of many of these by a develop- 
ing nervous system. This principle of appropriation I be- 
lieve to be as significant in elucidating the present condition 
of the nervous system and its appendages, as the principle 
of evolutionary sequence of parts, muscle, sense organ, and 
central nervous organ." ^ 

Description of the Nervous System 

Let us now consider in greater detail the principal char- 
acteristics of a fully developed nervous system as it is to 
be found in any one of the higher animals. We have noted 
that the receptor cell is more sensitive to external stimuli 
than other peripheral cells. This statement is, however, 
not quite accurate, for while a receptor is very sensitive to 
certain kinds of stimuli, it may be less sensitive than the 
ordinary cell to other stimuli. Thus a receptor is, as 
Sherrington puts it, "a mechanism more or less attuned to 
respond specially to a certain one or ones of the agencies 
that act as stimuli to the body." ^ This selective ex- 
citability of the receptors or sensory organs has undoubt- 

^ op. cit., p. 345. « op. cit., p. 12. 



The Evolution of the Nervous System 151 

edly arisen through adaptation and is of great utiHty to 
the organism. Because of the high degree of speciaHzation 
which has developed among these receptors, the organism 
can adjust itself with much more nicety to its surroundings. 
The functional value of these receptors is therefore very 
great. Sherrington has summed up the function of the 
receptor in the following words: ''The main function 
of the receptor is therefore to lower the threshold of excita- 
bility of the arc for one kind of stimulus, and to heighten for 
all others.^'' ^ 

This specialization on the part of the receptors is some- 
times described under the name of "the law of the specific 
energy of the sense organs." Loeb criticizes this law as 
follows: ''This so-called law of the specific energy of the 
sense organs is not pecuHar to the sense organs ; it appHes, 
as was emphasized by Sachs, to all Hving matter ; it even 
holds good for machines. It is in reality only another 
expression for the fact that the eye, the ear, and every living 
organ are able to convert energy in but one definite form 
— that is, that they are special machines." ^ This is all 
true enough, for it goes without saying that every particle 
of matter will transmit energy somewhat differently from 
every other particle of matter, for there are no two particles 
of matter which are absolutely aHke. But the difference 
between the way in which each sense organ transmits energy 
is so great from that of other kinds of protoplasm, and the 
functional value of these differences is of such importance, 
that it is, I believe, justifiable to emphasize these differ- 
ences by speaking of the specific energies of the sense organs. 

After a stimulus has been received by the receptor, it 

1 op. cii., p. 12. 2 Op. cit., pp. 290-291. 



152 The Science of Human Behavior 

must be conducted to the effector if it is to affect the be- 
havior of the animal. Sherrington states that nerve cells 
have to an unusual degree the power to conduct stimuli. 
''They have in exceptional measure the power to spatially 
transmit (conduct) states of excitement (nerve impulses) 
generated within them." ^ But this power arises not only 
out of the composition of the nerve cells, but also out of 
their shape. As has already been indicated, many of the 
nerve cells are elongated and stretch out long protoplasmic 
threads in the direction in which the stimulus is to travel. 
In some cases the stimulus may go all the way to the effec- 
tor by one nerve cell, though probably no such case exists 
in the higher animals. In such cases the conduction would 
be most rapid and with the smallest loss of force, for it is 
the passage from one cell to another which delays a stimulus 
and weakens it. But even if it has to pass through more 
than one nerve cell, the number will be much fewer than if 
they were ordinary cells, so that the conduction will be 
much more rapid and with smaller loss of force than if the 
conduction were by means of ordinary cells. 

The receptors or sense organs vary greatly amongst 
themselves. As we have already seen, in each case there 
is represented a characteristic of all protoplasmic matter 
which has become highly specialized in the cells of the 
sense organ. For example, the essential part of the eye 
consists of cells which have become highly sensitive to 
photic stimuH. As we have seen in a preceding chapter, 
a rudimentary eye is to be found even in the lowest organ- 
isms, such as some of the protozoa, in the form of a spot 
which is unusually sensitive to light. The sense organs 

> op. cit., p. 2. 



The Evolution of the Nervous System 153 

of taste and of smell consist of cells which are highly sen- 
sitive to chemical stimuli. The sense organs of touch and 
of hearing consist of cells which are highly sensitive to 
mechanical stimuli. Some of these sense organs have be- 
come highly complex mechanisms, such as the eye with its 
lens, cornea, retina, etc., and the ear with its otoliths, 
cochlea, circular canals, etc. I have not the space to de- 
scribe in detail how these organs have evolved, some sug- 
gestion of which has been given in preceding chapters, but 
must discuss how these organs are connected with the nerv- 
ous system. 

It will be noted that the sense organs are not necessarily 
nerve cells, just as we have already noted that the effectors 
are not nerve cells. As a matter of fact, most of the sense 
organs are not nerve cells. It will also be noted that the 
sense organs are necessarily peripheral ; that is to say, they 
are on a surface which is exposed to stimuli. This does not 
mean that they are necessarily on the outside of the body. 
Many of them are on the surface of the intestines and the 
other internal organs. But all of the sense organs are con- 
nected with effectors, in the higher animals at any rate, by 
means of nerves. 

Wundt states that a nerve ends in a peripheral organ in one of two 
ways. "The termination of a nerve in the peripheral organs may 
take one of two forms. Either the ends of the neuritic threads divide 
up into a fascicle or network of finest dendritic fibrils, that terminate 
freely along the elements of other, non-nervous tissues ; or the neu- 
ritic thread passes directly over into a terminal cell situated within 
or between the organs. The terminal cell may be an original nerve 
cell, pushed out towards the periphery of the body ; or it may have 
acquired this character later on in the course of development, by the 
penetration of a nerve fibril into an epithelial cell. The two forms of 
nerve termination occur side by side, in these their characteristic 



154 The Science of Human Behavior 

diflferences, in the different sense-organs, where they are evidently 
connected with essential differences in the mode of sensory excita- 
tion." ^ 

The first tj^je of nerve termination is illustrated in the termina- 
tion of sensory nerves in the skin where the neurite when it enters 
the epithelium breaks up into a reticulum of delicate fibrils. It is 
also illustrated in the nerve endings in muscles. The second type 
of nerve termination is illustrated in the organ of smell, in which every 
nerve fiber enters a nerve cell in the olfactory mucous membrane. 

The Neurone 

In order to understand more clearly how a stimulus is 
carried from receptor to effector, we must examine in more 
detail the nerve cell. As has already been indicated, a nerve 
cell is usually somewhat elongated and sometimes sends 
out fibers which attain great length. It has sometimes been 
thought that these fibers are not a part of the nerve cell. 
But it is easy to show that they are a vital, trophic, as well 
as a functional part, of the nerve cell, because if they are 
cut off from the central part of the cell they perish. Be- 
cause of this failure on the part of some to recognize that 
these fibers form a part of the nerve cell, it has become 
somewhat customary to call the nerve cell, including all of 
its appendages, a neurone } 

The neurones vary greatly in shapes and sizes, and so do their pro- 
cesses. In many neurones one of the processes is much longer than 
the rest and is called the neurite or axone or axis-cylinder or neuraxone 
or nerve process. Some of these neurites are very long as, for example, 
those which run from the spinal cord to the ends of the toes. Some 
neurites give off at intervals branches called collaterals or paraxones, 
which connect them with other neurones. The neurone has also 

' W. Wundt, Principles of Physiological Psychology, London, 1904, Vol. I, p. 47. 
* This term was coined by Waldeyer in 1891. See his paper in the Deut. Med' 
Wochenschrift, 1891, p. 50. 



The Evolution of the Nervous System 155 



Dendrites 



certain protoplasmic processes which are called dendrites or dendrons 
or cytodendrites. These dendrites are usually shorter than the 
neurites and are much branched. They serve like the collaterals to 
connect the neurones with each other and 
also to receive stimuli from receptors and 
conduct them to the neurones. It has 
been thought by some that the sole func- 
tion of the neurites is to conduct stimuli 
from the neurones to the effectors, but it 
appears now that they have other func- 
tions to perform as well. 



The exact mode of connection 
between the neurones is a matter 
of importance. As has been in- 
dicated, the connection is through 
the dendrites and collaterals. But 
inasmuch as each neurone forms a 
separate cell, it is thought by many 
that there must be a surface of sep- 
aration between the nerve cells just 
as there is between other types of 
cells. This is the synaptic theory 
of the connection between nerve 
cells.^ In this theory the junction 
between the neurones is called the 
synapse, and it is beheved that the 




Telodendrion 



cells are separated by a thin trans- Fig. 8.— Diagram of a typical 

. ^ . , neurone. (After Piersol.) 

verse membrane. It is, however, 

difficult to prove this theory because of the microscopic 

character of this membrane. Furthermore, it demands 

^ By some the synaptic theory is included as an essential part of the so-called 
"neurone theory" or "neurone doctrine." (See W. H. Howell, Textbook of Physiol- 
ogy, Philadelphia, 1906, pp. 121-123.) But it is questionable if the neurone neces- 
sarily involves the synapse. 



156 The Science of Human Behavior 

an explanation of how stimuli pass easily and rapidly 
through this membrane. Another theory of the connection 
between the neurones is the neurofibrillar or intercellular 
bridge theory according to which the neurones are connected 
by protoplasmic threads which pass directly from one cell 
to the other. This theory also is a difficult one to prove, 
but both of these theories have had considerable influence 
upon neurology. 

The Central Nervous System 

Most of the neurones are located in what is called the cen- 
tral nervous system. Just how this system evolved is hard 
to explain, and I have not the space to attempt to do so here. 
According to some writers the nerves were at first external 
and then withdrew into the interior of the body to form the 
central nervous system.^ According to some of the sup- 
porters of the synaptic theory, the central nervous system 
has come into being through the S3mapse. '' The synaptic 
nervous system has developed as its distinctive feature a 
central organ, a so-called central nervous system; it is through 
this that it brings into rapport one with another widely 
distant organs of the body, including the various portions 
of the diffuse nervous system itself." ^ 

But in whatever way the central nervous system may 
have evolved, we have to accept it to-day as an important 
part of the nervous system in the higher animals. Before 
ending this chapter I wish to describe briefly the central 
nervous system in vertebrates. 

The vertebrate central nervous system consists of the 

1 Cf. H. H. Wilder, History of the Human Body, New York, 1909, p. 465. 

2 Sherrington, op. cil., p. 312, 



The Evolution of the Nervous System 157 

spinal cord, which is divided up into segments which cor- 
respond with the segments of the spinal column, and the 
brain, which is made up morphologically of a number of 
segments of the spinal cord which have become highly 
differentiated. It is evident that the vertebrates have a 
great advantage over the invertebrates in developing the 
central nervous system, because of the serial arrangement 
of the parts of the organism. The results of this advan- 
tage are shown in two ways.^ In the first place, the central 
nervous organs of the vertebrates display a much greater 
number of long neurones over short ones. In the second 
place, the vertebrates possess a very much larger number of 
association neurones. It is also to be noted that in the 
later stages of the evolution of animals the central nervous 
system has evolved very rapidly and has thus furnished a 
basis for mental .evolution, while the sense organs have 
improved much less.^ The sense organs reached a high 
state of efficiency earlier in the evolution of animals and 
have not improved very much since. The eye in some 
kinds of fish is almost as good as that of the mammal, while 
the sense of hearing is very acute in some of the reptiles 
and amphibians. 

1 Cf. G. H. Parker, op. cU., p. 262. « Cf. H. H. Wilder, op. cit., pp. 465-466. 



CHAPTER IX 

THE FUNCTIONS OF THE NERVOUS SYSTEM 

The kinds of reflex arcs, 159. — Facilitation, 160. — Inhibition, 
160. — The common path, 160. — The integrative function of the 
nervous system, 161. — Mechanical, chemical, and nervous inte- 
gration, 161. — The functional divisions of the nervous system, 
162. — The origin of the head and brain, 163. — The functions 
of the distance receptors, 164. — Extero-ceptive, proprio-ceptive, 
and intero-ceptive receptors, 165. — The neuromeres, 167. — The 
divisions of the brain, 167. — The functions of the cerebellum, 168. 
— The functions of the cerebrum, 172. — The divisions of the cere- 
brum, 174. 

It is evident from the brief description of the evolution 
of the nervous system in the preceding chapter that we 
still have much to learn about this evolution. But what 
we do know is very suggestive with respect to the functions 
of the nervous system, so that the preceding chapter has 
incidentally thrown some Hght upon these functions. 

We still have much to learn, also, about the functions of 
the nervous system. But the subject is one of supreme 
importance in the study of behavior, especially with respect 
to the higher animals, because most of the actions of these 
animals are determined directly by the nervous system. 
Most if not all of the data presented in this chapter are 
certain, but some of the theories discussed are very uncertain 
and may be disproved. I shall begin the discussion of 
this subject by describing the different kinds of reflexes in 
the vertebrates. 

158 



The Functions of the Nervous System 159 



The Reflex Arc 

There are few if any reflexes in the vertebrates which do 
not pass through the central nervous system. Three levels 
of reflex arcs are sometimes distinguished.^ The first is 
an arc on the spinal level. In this arc the stimulus passes 
by means of the processes of a neurone from the receptor 
organ to the cell body of a sen- 
sory neurone in the central 
nervous system. From this 
neurone it is transferred to a 
neurone connected with the 
effector organ and by means 
of whose processes it is carried 
to the effector. The second 
level of arcs is where loops are 

formed on the arcs of the spinal Fig. 9. — Diagram iUustrating a reflex 

, , . . . , arc and showing fundamental xmits 

level by their neurones beCOm- of nervous system. ^, sensory neu- 

ing connected with each other ^°'^^> conducting afferent impulses 

. by its process (a) from periphery 

SO that these reflexes influence (S) ; B, motor neurone sending ef- 

each other. The third level is ^"'"^^ iraY>nhts by its process (.) to 

muscle. (After Piersol.) 

reached when the brain de- 
velops so that the reflexes become interconnected in a much 
more complex fashion. The cerebrum, which is the most 
important part of the brain, is made up largely of associa- 
tion centers ; that is to say, of neurones which are not di- 
rectly connected with receptor or effector organs, but whose 
processes are devoted entirely to connecting other neurones 
with each other. 
As a result of these connections established between 




Cf. W. McDougall, Physiological Psychology, London, 1905, pp. 20-21. 



160 The Science of Human Behavior 

neurones by means of the central nervous system, two very 
important phenomena takeplace.^ The first is facilitation ; 
that is to say, the reenforcement of the excitement of a 
motor system by the stimulation of other sensory neurones 
connected with the same motor system. The second is 
inhibition, or the partial or complete prevention of the 
spread of excitement from a sensory neurone to a motor 
system, caused apparently by the simultaneous excitement of 
some other motor system. A sensory neurone can receive 
stimuH only from the sense organ with which it is connected. 
But an effector may receive stimuli from several sensory 
neurones. These facts have been stated in what Sherring- 
ton calls the principle of the common path, which is that 
^' while the receptive neurone forms a private path exclu- 
sively serving impulses of one source only, the final or effer- 
ent neurone is, so to say, a public path, common to impulses 
arising at any of many sources of reception." ^ This 
common path may be used by like reflexes at the same time, 
but not by unHke reflexes, for an effector cannot be made 
to do two things at the same time. " Unlike reflexes have 
successive hut not simultaneous use of the common path; like 
reflexes mutually reenforce each other on their common path.^^^ 
These characteristics of the common path make it a co- 
ordinating mechanism which prevents confusion by re- 
stricting the use of the effector to one action at a time. 
^^The resultant singleness of action from moment to moment 
is a keystone in the construction of the individual whose 
unity it is the specific office of the nervous system to perfect. 
The interference of unlike reflexes and the alliance of Uke 

' Cf. Wundt, op. cit., pp. 70-77; McDougall, op. cit., pp. 35-36; Sherrington, 
op. cit., p. 36. * Op. cit., p. 116. » Op. cit., p. 233. 



The Functions of the Nervous System 161 

reflexes in their action upon their common paths seem to 
lie at the very root of the great psychical process of * atten- 
tion/ "^ 

Integration 

The coordination effected by the common path brings 
our attention forcibly to the main function of the nervous 
system in general; namely, its integrative function. I 
have already referred to this function, and it has been il- 
lustrated over and over again in the preceding description 
of the nervous system. Indeed, in a sense the integrative 
function includes all the other functions of the nervous 
system. The best exposition of this subject has been made 
by Sherrington in his able work entitled The Integrative 
Action of the Nervous System, which has already been cited 
a number of times, and I shall follow his treatment in the 
main in this discussion. 

There are several forms of integration in the animal 
organism. There is first the mechanical combination of the 
cells of the body into a single mass by means of muscles, 
connective tissue, etc. In the second place integration is 
effected by means of certain chemical agencies which es- 
tablish communication between different parts of the organ- 
ism. We find these agencies in the reproductive organs, 
in the digestive organs, and in the circulation of the blood. 
Both of these forms of integration are of great importance 
and indirectly affect very greatly the behavior of the animal. 
But the form of integration which is of most interest to us 
is the integrative action of the nervous system, because this 
determines directly and to a large extent the behavior of 
the animal. 

» op. cit., p. 234. 



162 The Science of Human Behavior 

In its integrative action the nervous system "works 
through living lines of stationary cells along which it 
dispatches waves of physico-chemical disturbance, and 
these act as releasing forces in distant organs where they 
finally impinge." ^ The result is that nervous integration 
is usually more rapid than the other forms of integration 
in which the means of communication is intercellular ma- 
terial, such as connective tissue, or where material in mass 
has to be transferred, as in the circulation of blood. The 
unit mechanism in nervous integration, as in the nervous 
system as a whole, is the reflex arc, "because every reflex 
is an integrative reaction, and no nervous action short of a 
reflex is a complete act of integration." ^ Nervous inte- 
gration is therefore accompHshed entirely by means of re- 
flexes, of which two kinds may be distinguished, the simple 
reflex, of which there are none, probably, at any rate in 
the higher animals, and the compound reflex. All or most 
of the behavior of the higher animals is therefore reflex, 
because all or most of it is integrated by the nervous sys- 
tem. There are differences of opinion as to this which 
will be discussed in the chapter on consciousness. 

Functional Divisions of the Nervous System 

The functional divisions of the nervous system are the 
somatic sensory, the somatic motor, the visceral sensory, 
and the visceral motor .^ The visceral nerves, sometimes 
called the sympathetic system, are not under voluntary 
control, and it was formerly believed that they were not 
connected with the other parts of the nervous system which 

1 op. cit., pp. 3-4. ' Op. cit., p. 7. 

' Cf. J. B. Johnston, The Nervous System of Vertebrates, Philadelphia, 1906, pp. 
101-103. 



The Functions of the Nervous System 163 

are under voluntary control, but it is now known that such 
connections exist.^ As has already been stated, the cen- 
tral nervous system in vertebrates is divided into segments 
called neuromeres, which correspond with the segments or 
metameres of the spinal column. In other types of animal 
organisms, also, we find a segmental arrangement, as, for 
example, in many radiates. But a higher development has 
been possible in the species in which the segments are ar- 
ranged serially. In a radiate each segment bears the same 
relation to the common axis and to the other segments, so 
that there is not much chance for differentiation. For 
example, the mouth is at the same distance from all the 
segments, and in other ways the conditions of life for each 
segment are about the same as for all. But in a serially 
segmented animal there is much opportunity for differen- 
tiation among the segments.^ For example, the segments 
from which the limbs begin are sure to develop a more 
complex nervous mechanism. The segments are no longer 
equidistant from the mouth. Most important of all, 
certain segments now go first in locomotion, and conse- 
quently develop far beyond any other segment. This 
marks the beginning of the head and the brain, which I 
shall now discuss. 

It is easy to see how the leading segments would develop 
much farther than the other segments. In the first place, 
more impressions fall upon these segments, thus developing 
them more than the other segments in the individual. 
Unless, however, these effects upon these segments in the 
individual were transmitted by inheritance, they would have 
no effect upon the species. In all probabiHty they are not 

1 Cf. McDougall, op. cU., p. i6. * Cf. Sherrington, op. cit., p. 315. 



164 The Science of Human Behavior 

transmitted, but there are other forces at work to cause 
greater development of these segments in the species. 
These segments are the first ones usually to meet the forces 
of the environment which are beneficial or harmful to the 
animal. Consequently, these segments are subjected to a 
very rigorous process of selection, and only those individ- 
uals tend to survive whose receptors in the leading seg- 
ments adapt them to their environment. This results in 
the refinement of these receptors until they are highly 
adaptive. 

Distance Receptors 

Especially significant in this process is the evolution of 
what Sherrington calls the ^^distance-receptors,''^ by which 
he means ''receptors which react to objects at a distance." ^ 
In one sense no receptor could be a distance-receptor, be- 
cause every receptor reacts directly to mechanical forces 
which act upon it. Thus receptors which are reacting to 
photic stimuli react directly to vibrations in the ether; 
receptors which react to auditory stimuli react directly 
to vibrations in air or water or whatever the conducting 
medium is. In this respect they are similar, for example, 
to tango-receptors, which react directly to massive, material 
objects which come into contact with them. But they are 
distance-receptors in the sense that they determine reactions 
which adapt the individual to objects which are at a dis- 
tance, but from which are emanating forces which directly 
affect the receptors. 

So it is that a number of these distance-receptors begin 
to develop on these leading segments. ''The retina is thus 

» Op. cit., p. 324. 



The Functions of the Nervous System 165 

a group of glorified 'warm spots/ the cochlea a group of 
glorified 'touch spots.* Again, a group belonging to the 
system adapted to chemical stimuli reach in one of the 
leading segments such a pitch of delicacy that particles in 
quantity unweighable by the chemist, emanating from sub- 
stances called odorous, excite reaction from them." ^ The 
organs of vision, hearing, and smell are the principal ones of 
the distance-receptors. In the case of smell, as indicated 
above, the sense organ is acted upon by minute particles so 
that it may appear that it is not a distance-receptor. But 
these objects acting upon the organ cause the individual to 
adapt itself to the object at a distance from which these 
particles are emanating, so that this sense organ may be 
called a distance-receptor. 

Just how the animal organism has acquired the abiHty 
to adapt itself to these objects at a distance, it is difiicult to 
explain. Sherrington says that these receptors "initiate 
sensations having the psychical quaHty termed projicienceJ^ ^ 
That is to say, these sensations are projected into the world 
outside the individual, and this pro jicience "refers them, 
without elaboration by any reasoned mental process, to 
directions and distances in the environment fairly accurately 
corresponding with the 'real' directions and distances of 
their actual sources." This property of pro jicience belongs 
only to sensations initiated by what Sherrington calls the 
"extero-ceptive" receptors. By extero-ceptive he means 
those which lie on the surface of the body, and distinguishes 
them from the proprio-ceptive receptors, which lie buried 
beneath the surface, and the inter o-ceptive receptors, which 

1 op. cit., p. 324. 

* Op. cit., p. 324. Here, as elsewhere in his writings, Sherrington uses psychologi- 
cal terms in a rather loose fashion. 



166 The Science of Human Behavior 

line the surfaces of the internal organs. It is evident that 
the distance-receptors would have to be extero-ceptive, 
because the proprio-ceptive and intero-ceptive receptors 
hidden beneath the surface could not very well be affected 
by the forces emanating from the objects at a distance to 
which the individual reacts. 

That these distance-receptors have great survival value, 
must be quite evident. With the aid of them an animal 
becomes aware of, and is thus able to avoid, the objects 
which are injurious to it and to bring itself into contact 
with those which are beneficial to it. Thus the head, 
which is constituted of these leading segments in which 
most of the distance-receptors are located, is of the greatest 
importance to the animal, because it "moves habitually 
into that part of environmental space which has been al- 
ready explored by the distance-receptors of its own leading 
segments," and inasmuch as the head ''has the mouth, it 
takes in the food, including water and air, it has the main 
receptive organs providing data for the rapid and accurate 
adjustment of the animal to time and space. To it the 
trunk, an elongated motor organ with a share of the di- 
gestive surface, and the skin, is appended as an apparatus 
for locomotion and nutrition. The latter must of necessity 
Ue at the command of the great receptor-organs of the 
head." ^ 

The Brain 

But so far have been discussed only the receptor organs 
of the head, and most if not all of these are not nerves, so 
that there still remains to be discussed the nervous equip- 

* op. cit., p. 350. 




Prosencephalon 

(fore-brain) 



Mesencephalon 
(mid-brain) 



Cerebrum 



Olivary body 



- - Cerebellum \ 

I Metencephalon 
^Fons (Varolii) J (hind-brain) 

Myelencephalon 
(medulla oblongata) 



Rhomben- 
cephalon 



Encephalon 

(brain) 



" Pars cervicalis 



Pars thoracalis 



It- Pars lumbalis 



Pars sacralis or 
conus medullaris 



Spinal cord 
(medulla spinalis) 



Fig. ic, — Diagram illustrating the divisions of the central nervous system. (After 

Morris.) 



The Functions of the Nervous System 167 

ment of the head. This equipment consists of the neuro- 
meres or sections of the spinal cord which correspond to the 
segments of the spinal column from which evolve the skull 
or bony inclosure of the head. These neuromeres have 
developed so greatly as to be very large and complex as 
compared to their original state. This development is due 
to the same causes as the enlargement of the sections of the 
spinal cord where the fibers from the Hmbs come in. The 
neuromeres of the leading segments receive stimuli from 
many more receptors than do most of the neuromeres of the 
spinal cord. Furthermore, many of these are distance- 
receptors from which are received sensations for which 
many association paths are established. 

The neuromeres of the head constitute the brain. The 
brain consists of four parts — the cerebrum, the cerebellum, 
the pons VaroKi, and the medulla oblongata. The medulla 
oblongata connects the spinal cord with the pons, and the 
pons connects the other three parts of the brain with each 
other. The most important parts of the brain are the 
cerebrum and the cerebellum, and I shall now discuss their 
functions briefly. 

It is reasonable to suppose that in a part of the body 
which is so highly differentiated as is the brain, there must 
be a considerable differentiation of function. This would be 
in accordance with what we see of the physiological divi- 
sion of labor in other parts of the organism. But while 
there has been a great deal of investigation of this subject, 
there is still great uncertainty as to the exact functions of 
these parts of the brain. There are difficulties involved in 
every method of research used in studying this problem. 
The anatomical method of studying the anatomy of the 



168 The Science of Human Behavior 

brain furnishes certain presumptions as to how the functions 
are distributed among the parts of the brain. But the 
information thus gained is not certain, because such ana- 
tomical study cannot be carried on to a very great extent in 
the Kving subject, so that most of these researches are made 
when the brain is not functioning. The method of ex- 
tirpation is a vahiable one, but is not ahvays a certain one, 
because the surgical effect of the shock of the operation may 
be such as to cause changes greater than the mere effect 
of the extirpation. Furthermore, other parts of the brain 
sometimes compensate for the parts which have been extir- 
pated, so that it is impossible to tell exactly what are the 
functions of the extirpated parts. Many more researches 
will have to be made before the exact functions of all parts 
of the brain can be known. I shall therefore limit myself to 
citing the opinions of a number of authorities as to the 
functions of the cerebellum and the cerebrum. 

The Cerebellum 

Herbert Spencer in his famous treatise on psychology 
suggested that ^'the cerebellum is an organ of doubly-com- 
pound coordination in space; while the cerebrum is an 
organ of doubly-compound coordination in time.^^ ^ He 
beheved that this theory was supported by the facts that 
*'the cerebellum is unusually developed in birds of prey, 
which have to coordinate with great accuracy the relations 
of distance, direction, and complex form, as well as very 
precisely to coordinate the involved movements appro- 
priate to these involved impressions. And there is, on the 
other hand, the fact that the cerebrum predominates in 

' Principles of Psychology, 3ci edit., New York, 1895, Vol. I, p. 61. 



The Functions of the Nervous System 169 

creatures showing, like ourselves, the power of adapting, 
throughout long periods, concatenated compound actions 
to concatenated compound impressions." ^ This is a 
rather plausible theory because of the relative positions of 
these two parts of the brain. The cerebellum is behind 
and somewhat below the cerebrum and is an enlargement of 
certain segments of the spinal cord back of the segments 
from which the cerebrum has developed, these being the 
first segments of the spinal cord. The cerebellum therefore 
receives stimuli from the spinal cord before they reach the 
cerebrum, and is able to make simpler reactions, such as 
may involve coordinations with respect to space. The cere- 
brum is reached later and makes the more complex coor- 
dinations of sequence, such as are involved with respect to 
time. But this is too simple a theory by which to explain 
the differentiation of functions in the brain, and I shall 
now pass on to some of the later theories. 

There has been much difference of opinion as to the 
fimctions of the cerebellum. Some have overestimated 
and others have underestimated its importance, and there 
is much imcertainty both as to the importance and the 
nature of its functions. But there appears to be a rather 
widespread opinion that it has a direct control over the 
movements initiated in the cerebrum, and serves to coor- 
dinate these movements. Thus Wundt speaks as follows : 
"The cerebellum appears to be intended for the direct reg- 
ulation of voluntary movements by sense impressions. If this 
hypothesis be correct, it will, accordingly, be the central 
organ in which the bodily movements incited from the cer- 
ebrum are brought into harmony with the position of the 

* Op. cit., p. 62. 



170 The Science of Human Behavior 

animal body in space. This conception agrees sufficiently 
well with our anatomical knowledge of the course of the 
Hues of conduction, incoming and outgoing." ^ 

Johnston expresses a similar opinion, giving concrete examples of 
the effect of its extirpation in animals. "What then is the function 
of the cerebellar cortex? Disease of the cerebellum in man and its 
extirpation in animals always results in disturbances of voluntary 
muscular action. Animals from which one hemisphere or the whole 
cerebellum has been removed are unable to stand or walk until they 
have learned to make compensatory efforts. Does the cerebellum 
have the special function of maintaining the equilibrium, or is it 
necessary for the coordination of muscular contractions with refer- 
ence to definite movements ? In the results of experimental investi- 
gations on mammals the function of the cerebellum which stands out 
most prominently is different from either of these. Dogs which have 
lost one cerebellar hemisphere, although they are unable to stand or 
walk, can swim well in water (which supports their body weight), 
both coordinating their movements and maintaining their equilibrium. 
Such animals learn after a time to compensate for the loss of the cere- 
bellum by certain voluntary modifications of their movements ; e.g., 
curving the spine so as to bring the center of gravity over the sound 
legs, spreading the feet wide apart, etc. They can then stand and 
walk. These and other facts show that the loss of the cerebellum 
does not involve loss of the power of equilibration nor of cutaneous 
or muscle sense, on which the power of coordinated movements de- 
pends, but does result in weakness of muscular action on the injured 
side. It seems, therefore, that the cerebro-spinal mechanisms are 
sufficient to carry out all voluntary movements without the aid of 
the cerebellum, but the movements are lacking in strength, precision, 
and regularity. The cerebellum is not shown to be a necessary link 
in the nervous mechanisms which control muscular action, but it 
seems to add something to the voluntary movement. According to 
Luciani the function of the cerebellum is to maintain the tone of mus- 
cles during rest, to increase the energy of contraction when called 
forth by voluntary impulses, and to determine the rhythm of motor 
impulses. In this way the imperfect actions of the dog deprived of 

1 Op. cit., p. 276. 



The Functions of the Nervous System 171 

its cerebellum would be perfected into normal movements. Whether 
the cerebellum cortex actually serves other functions, such as the coor- 
dination of specific movements, remains for further investigation to 
decide." ^ 

Sherrington suggests that the cerebellum is the head 
ganglion of the proprio-ceptive system. It has already 
been indicated that the term proprio-ceptive as used by 
him refers to the receptors buried beneath the surface. He 
says that the central nervous organ of any system of nerves 
is likely to be located at the point where the largest number 
of nerves from that system enters the central nervous sys- 
tem. It appears that this is true for the cerebellum with 
respect to the proprio-ceptive system, for in the cerebellum 
"converge internuncial paths stretching to this mecha- 
nism from the central endings of various proprio-ceptive 
neurones situate in all the segments of the body. There 
afferent contributions from the receptors of joints, muscles, 
ligaments, tendons, viscera, etc., combine with those from 
the muscular organs of the head and with those of the laby- 
rinthine receptors themselves. A central nervous organ 
of high complexity results. Its size from animal species to 
animal species strikingly accords with the range and com- 
plexity of the habitual taxis of the skeletal musculature. 
This central organ is the cerebellum." ^ Sherrington be- 
lieves that this theory harmonizes with Spencer's theory, 
which has been cited ; namely, that the cerebellum is the 
organ for coordination in space, and with the later theory 
which has been illustrated from Wundt and Johnston; 
namely, that it is the organ for the coordination of voluntary 
movements. Inasmuch as many of the proprio-ceptive 

* op. cit., pp. 249-250. 2 Qp^ cit., p. 348. 



172 The Science of Human Behavior 

receptors are located in the muscles, tendons, joints, etc., 
which directly determine the movements of the body, it 
seems plausible that the central nervous organ of the pro- 
prio-ceptive system should have a large measure of control 
over the movements of the body. 

The Cerebrum 

The cerebrum is the largest and the most important 
nervous organ in the highest animals. All writers on the 
brain agree in attributing great importance to the cerebrum, 
though their theories as to why it is so important vary 
somewhat. Wundt says, after describing the effects upon 
the individual of the extirpation of the cerebrum, that 
'Hhese final abrogation phenomena lead us to the general, 
and, we must also admit, indefinite conclusion that the 
intelligence, the higher affective processes, and the compound 
voluntary actions are conditioned upon the integrity of the 
cerebral hemispheres." ^ He states further that this con- 
clusion drawn from the phenomena of abrogation is con- 
firmed by results from comparative anatomy, evolutionary 
biology, and anthropology. ''Comparative anatomy shows 
that the mass of the cerebral lobes, and more especially 
their superficial ridging by fissures and gyres, increase with 
increasing intelligence of the animal. This law is, however, 
limited by the condition that both factors, mass and su- 
perficial folding, depend primarily upon the size of the 
body." ^ This is a well-known fact for which much evidence 
has been gathered. For example, the average brain weight 
of a man's brain in European races is 1360 grams, and that 
of a woman's brain of the same races is 1211 grams, while 

' op. cU; p. 284. » op. cit., p. 286. 



The Functions of the Nervous System 173 

the average brain weight of the great anthropoid apes 
(gorilla, chimpanzee, and orang-utan) is only 360 grams. ^ 
Thus in the orang-utan the brain represents only one half 
of one per cent of the body weight, while in European 
man the proportion is at least three per cent. 

Sherrington states an interesting theory to the effect that 
the cerebrum is the ganglion of the distance-receptors. We 
have already seen that he considers the cerebellum the head 
gangKon of the proprio-ceptive system. The cerebrum 
would then be the ganglion of those extero-receptors which 
receive stimuH from a distance. He states that the reflexes 
which start from the distance-receptors are connected with 
the cerebrum, and that if the cerebrum is extirpated the 
reactions which are stimulated by these receptors are 
destroyed in large part. "The distance-receptors are the 
great inaugurators of reaction. The reduced initiation of 
action which ensues on ablation of the cerebrum seems ex- 
pKcable by that reason. The curtailment which ensues 
is indicative of damage which their removal inflicts on re- 
actions generated by the distance-receptor organs. By a 
high spinal transection the splendid motor machinery of 
the vertebrate is practically as a whole and at one stroke 
severed from all the universe except its own microcosm and 
an environmental film some millimeters thick immediately 
next its body. The deeper depression of reaction into which 
the higher animal as contrasted with the lower sinks when 
made spinal signifies that in the higher types more than in 
the lower the great distance-receptors actuate the motor 
organ and impel the actions of the individual. The deeper 
depression shows that as the individual ascends the scale 

1 J. Deniker, The Races of Man, London, igoo, pp. 17-18. 



174 The Science of Human Behavior 

of being, the more reactive does it become as an individual 
to the circumambient universe outside itself." ^ 

The cerebrum is divided into hemispheres, and these hemispheres 
may be divided into three parts. The first part connects the cere- 
brum with the rest of the brain and is a thick bi-lobed mass consist- 
ing of groups of nerve cells through which pass many large bundles of 
fibers. This part is called the basal gangHon or corpus striatum. 
"Lying in front of and below the corpus striatum and forming part 
of the lower and mesial wall of the hemispheres at the anterior end 
are the olfactory bulb and olfactory lobe. On the ventral surface of 
the striatum is the nucleus amygdalce, which is continuous caudally 
with the pyriform lobe and the hippocampus in the temporal region 
of the hemisphere. These several structures, together with the 
fornix and hippocampal commissure, constitute the second main por- 
tion of the hemisphere, and may be spoken of collectively as the cen- 
tral olfactory apparatus. All the rest — much the greater part — of 
the cerebrum is concerned with sensory impulses from the external 
world which come from various parts of the body, including the special 
sense organs of sight and hearing ; with the correlation of these im- 
pulses with one another and with habitual tendencies produced by 
previous actions ; with voluntary impulses sent out to arouse, direct, 
or inhibit actions in response to stimuli ; with sensations ; and with 
thought processes. This portion of the cerebral hemispheres may be 
spoken of as the somatic pallium.'' ^ 

We are most interested in the pallium or cerebral cortex 
in which the highest functions of the brain are performed. 
The study of this part of the cerebrum is in the main the 
study of cerebral localization ; that is to say, the study of 
how these functions are locaHzed in the brain. I shall take 
up this subject in the next chapter. 

1 Op. cii., pp. 351-352. • Johnston, op. cit., p. 293. 



CHAPTER X 

CEREBRAL LOCALIZATION 

Phrenology, 175 — Anatomical study of cerebral functions, 176, 
— The anatomy of the brain, 177. — White and gray matter, 
178. — The cerebral cortex, 178. — Theories of cerebral localiza- 
tion, 179. — The association areas, 181. — The cerebral fibers, 
185. — Physiological study of the cerebral functions by stimula- 
tion and extirpation, 188. — CHnico-pathological study of cerebral 
functions, 191. — Functional and organic diseases of the brain, 
194. 

The idea that functions are localized in different parts of 
the brain is an old one. It was held by the representatives 
of the pseudo-sciences of physiognomy and phrenology 
(phrenology being a branch of physiognomy) . The phrenol- 
ogists beheved that they could tell the mental character- 
istics of an individual from a study of the conformation 
of his cranium. They did not mean by this that these 
mental characteristics are determined directly by the shape 
of the cranium, but that the cranium indicates the nature 
of the brain where these characteristics are determined. 
It is true that the cranium may give some slight indications 
as to the nature of the brain it incloses. But these indi- 
cations are at best very crude and are likely to be very 
misleading. So that in course of time physiognomy and 
phrenology became thoroughly discredited as furnishing 
scientific data as to the nature of the brain. Reacting from 
these pseudo-scientific theories it was the tendency of phys- 
iologists for a time to deny the existence of cerebral local- 

175 



176 The Science of Human Behavior 

ization and to believe that each organ in the brain acted as 
a whole. Thus, according to this theory there would be no 
localization of function within the cerebrum, but the whole 
of the cerebrum would be involved each time it functioned. 
However, recent methods of investigation have furnished 
a good deal of evidence of cerebral locaUzation, and these 
data will now be discussed. 

Methods of Studying Cerebral Functions 

There are three principal methods of studying the func- 
tions of the cerebrum ; namely, the anatomical, the phys- 
iological, and the cHnico-pathological.^ The anatomists 
dissect the nervous system and determine the distribution 
of the nerve cells and trace the paths of the nerve fibers. 
From such study many inferences, some of which are quite 
trustworthy, may be drawn as to the functions of the dif- 
ferent parts of the nervous system. For example, if it were 
known that a certain effector was not connected at all by 
a nerve with a certain central organ, it would be reasonable 
to suppose that the effector was not governed in any way 
by that organ. The nervous system is so complex and, as 
we have seen in the last two chapters, is so thoroughly 
integrated, that it is doubtful if there is any effector that is 
wholly unconnected with any central nervous organ. But . 
if the connection was indirect and very shght, it would be 
reasonable to suppose that the degree of control of the 
central organ over the effector was very slight. In similar 
fashion if an effector was connected very directly and by many 

^ Cf. Shepherd I. Franz, On the Functions of the Cerebrum: The Frontal Lobes, in 
the Archives of Psychology, Vol. I; and The Functions of the Cerebrum, in the Psy- 
chological Bulletin, Vol. VIII, No. 4 (April 15, 191 1). 



Cerebral Localization 177 

fibers with a central nervous organ, it would be reasonable 
to suppose that the central organ had a high degree of con- 
trol over the effector. 

Physiological research includes the methods of stimula- 
tion and extirpation. By stimulating parts of the nervous 
system and observing the motor and vascular reactions 
obtained, functional relations between different parts of the 
nervous system and effectors may be determined. By ex- 
tirpating parts of the nervous system and then observing 
the effect upon the behavior of the individual, inferences 
may be drawn as to the functions of the parts extirpated. 
The extirpation method is of chief value for the study of 
the parts of the cerebrum which are not excited by direct 
stimuH. The study of pathological conditions in the brain 
may throw much Hght upon the problem of cerebral local- 
ization. If a lesion of a certain part of the brain is fol- 
lowed by a derangement in the behavior of certain effectors, 
it is reasonable to suppose that there is a functional relation 
between that part of the brain and those effectors. 

By means of the methods of research described above, a 
vast amount of data has been gathered with regard to the 
cerebrum, and I can cite only a few general conclusions from 
some of the leading investigators. 

Anatomy of the Brain 

First let us note a few general anatomical facts. The brain, or 
encephalon, is developed from three embryological divisions ; namely, 
the anterior, the middle, and the posterior brain vessels or vesicles, 
which are at the anterior end of the neural tube. The anterior vesicle 
becomes the fore-brain, or prosencephalon. The middle vesicle be- 
comes the mid-brain, or mesencephalon. The posterior vesicle becomes 
the rhombencephalon. In the course of embryological development 



178 The Science of Human Behavior 

a constriction appears in the anterior vesicle and another in the pos- 
terior vesicle, so that each of these become divided into two, and there 
are five secondary brain vesicles in the place of the primary three 
vesicles. The fore-brain, or prosencephalon, becomes divided into 
the end-brain, or telencephalon, and the inter-brain, or diencephalon. 
The rhombencephalon becomes divided into the hind-brain, or meten- 
cephalon, and the after-brain, or myelencephalon. The cerebrum in- 
cludes all of the fore-brain and mid-brain, and the rhombencephalon 
includes the other parts of the brain. The three primary brain vesi- 
cles are at first in a straight line like the rest of the neural tube. But 
early in embryological development they begin to curve, so that in 
course of time they assume the rounded form of the brain.* 

The cerebrum, like the rest of the cerebro-spinal system, 
is composed of white and gray matter. The white matter 
is made up chiefly of bundles of medullated axones. The 
gray matter is composed chiefly of cell bodies and dendrites. 
It is evident, therefore, that stimuli from receptor sense 
organs must terminate in the gray matter, and impulses to 
effector organs must start from the gray matter, while these 
stimuli and impulses must be carried in large part by the 
white matter. The cerebral gray substance may be divided 
into three groups ; namely, the cortical, the ganglionar, and 
the central or ventricular. The cortical gray substance is 
of most interest to us, for here are determined in the main 
the actions of the individual which involve psychic quali- 
ties. 

The cortex of the cerebrum has been described in the following words: 
— "The exterior surface of the fore-brain is composed of a thin sheet 
of gray matter varying in thickness from one sixth to one quarter 
of an inch. That gray matter forms a barklike covering for the 

1 Cf. on the anatomy of the brain : H. E. Santee, Anatomy of the Brain and Spinal 
Cord, Philadelphia, 1907 ; Johnston, The Nervous System of Vertebrates, Philadelphia, 
1906; L. V. Barker, The Nervous System, New York, 1899; Wundt, Principles of 
Physiological Psychology, Vol. I, London, 1904 ; Howell, A Textbook of Physiology, 
Philadelphia, 1906, chaps. IX-XI. 



Cerebral Localization 179 

underlying white substance and is, therefore, called the cortex. It is 
thrown into irregular elongated folds named convolutions, or gyri, by- 
deep linear depressions, which greatly increase the relative amount of 
cortical substance. The linear depressions are called fissures, or 
sulci; and, in consequence of them, the gray substance is increased 
in bulk to fifty-eight and one half per cent of the entire cerebrum 
(De Regibus)." ^ This statement that the gray matter constitutes 
more than half of the cerebrum sounds rather exaggerated when we 
consider that in the hemispheres the gray matter is only the super- 
ficial covering of the cerebrum, but when the ganglionar and ven- 
tricular gray substances are added, this statement may be correct. 

The white matter of the cerebrum is composed in the adult of 
medullated fibers. These cerebral fibers form three systems: (i) 
projection or peduncular fibers, (2) transverse or commissural fibers, 
(3) association fibers.^ The projection fibers are connected only 
with the motor and sensory areas of the cerebral cortex and are, con- 
sequently, motor and sensory in function. The commissural fibers 
connect opposite sides of the cerebrum. The association fibers con- 
nect parts of the same hemisphere. We shall refer again to these 
systems of fibers after having studied in more detail the cerebral 
cortex. 

Anatomical Theories oe Cerebral Localization 

As has already been indicated, the phrenologists formu- 
lated a theory of the localization of functions in the brain 
and in the cerebrum in particular. But their theory was 
quite untenable in the light of further scientific researches. 
These functions as localized in the brain they termed "in- 
ternal senses." Gall distinguished twenty-seven of these, 
and his pupil Spurzheim increased the number to thirty- 
five. Some of these senses were most preposterous, such 
as the sense of facts, the fear of God, philoprogenitiveness, 
poetic talent, the impulse of self-preservation, etc. Re- 
acting from those pseudo-scientific ideas, the physiologists 

» Santee, op. cit., pp. 51-52. ' Santee, op. cit., pp. 224 ff. 



180 The Science of Human Behavior 

tended for a time to the belief that the cerebrum acted as a 
whole in performing its functions like certain other organs 
of the body, such as the heart, the lungs, etc. In similar 
fashion they believed that the other parts of the brain, such 
as the cerebellum, the medulla oblongata, etc., also per- 
formed their functions each as a whole. And some of the 
experiments of extirpation seemed to confirm this belief, for 
it was found in some of these experiments that when a part 
of the cerebrum was extirpated, the cerebral functions were 
weakened as a whole, but no functions were completely 
abrogated. But as more knowledge was acquired with 
regard to the structure of the brain and the course of con- 
duction paths, and as pathological observations were made 
of the results from local lesions in the cerebrum, the modern 
theories of cerebral localization were formulated. It goes 
without saying that these modern theories do not postulate 
specific centers for any such complex characteristics as did 
the phrenologists. The determination of each one of those 
characteristics would require the cooperation not only of 
many parts of the brain, but of other organs of the body as 
well. 

Wundt says, looking at these theories from the psychological 
point of view, that the terms "sensation" and "idea" now represent 
the two fundamental forms of psychical process in the place of the 
internal senses of the phrenologists. " * Sensation ' means in this 
connexion, any conscious reaction evoked by external sensory stimuli, 
while 'idea' includes, in accordance with the nomenclature of the 
older psychology, all kinds of 'memory image.'" On this basis two 
theories of localization have developed. "From these general prem- 
isses, the doctrine of locaHsation or, as its close relations to the 
older phrenological theories justify us in calling it, 'modern phre- 
nology ' has developed in two directions. In both forms, it is based upon 
the assumption that the cerebral cortex is divided up into a number 



Cerebral Localization 181 

of sensory centres, in which the excitations brought in along the 
sensory conduction paths release the specific sensations. . . . 
The one form of the doctrine of localisation asserts that the centres 
of sensation and idea are strictly connected, so that every sensory 
centre covers both processes, and the entire cortical surface is there- 
fore essentially composed simply of a number of adjacent sensory 
centres. . . . The second form of the locaHsation doctrine differs 
from the first mainly by its assertion that the central areas which 
subserve the colligation of sensations, and therefore also the retention 
of ideas, the centres, in fact, which underlie the complex psychical 
functions at large, are spatially separate from the sensory centres, 
though connected with them by manifold systems of association fibres. 
It accordingly gives this second order of centres, whose office it is to 
colligate the various sense departments, the special name of 'associ- 
ation centres' ; and we may therefore designate the second form of 
the localisation theory briefly as the ' theory of association centres. * " ^ 

Let us now consider some of the schemes of cerebral 
localization prepared by anatomists. As has already been 
indicated, part of the cerebral cortex is devoted to receiving 
stimuli from receptor organs and sending impulses to effec- 
tor organs. This part is divided up into several areas 
which are usually called the sensori-motor or senso-motor 
areas. Another and larger part of the cortex is devoted 
to establishing associations between the sensory and motor 
centers. This part is divided up into what are called the 
association centers. 

Johnston describes the senso-motor areas as follows: — "The 
afferent or sensory fibers which come to the neopallium ^ from 
lower brain centers end in certain regions, and from these regions 
alone (Flechsig) arise the great majority of the efferent or motor 
fibers which carry impulses to the motor centers of the brain and 
spinal cord. Hence these regions are given the name of the senso- 
motor areas. Three sensory centers are recognized, the visual, the 
auditory, and the somcssthetic areas. The last is the area for general 

1 Wundt, op. cit., p. 289. * The neopallium is a part of the cerebral cortex. 



182 The Science of Human Behavior 

bodily sensations. Since motor tracts descending from the visual 
and auditory fields are not well known, a general area corresponding 
roughly to the somassthetic area is commonly known as the motor 
area. The only way of describing the limits of these areas is by 
means of the superficial sulci and gyri of the brain. "^ He then 
describes the location of the somaesthetic area, the visual area, the 
auditory area, the gustatory area, and the motor area which, he says, 
"is practically coextensive with the somaesthetic area." These 
areas form about one third of the cortex. The remaining two thirds 
is taken up by the association areas. "The remaining two- thirds 
of the cortex is intercalated between the several senso-motor areas 
so that each of them is separated by a considerable space from the 
others. This whole area constitutes, according to Flechsig, the asso- 
ciation centers, and it may be divided into three main fields, the an- 
terior, middle, and posterior association fields ^ ^ Johnston defines 
the functions of these association areas more specifically as follows : 
"By association fields must not be understood areas in which the 
functions of association are carried out without the aid of the senso- 
motor areas. This would be physically impossible, and the term cor- 
relation centers would more truly express the function of the associa- 
tion fields. In other words, the function of the association centers 
is to correlate the actions of the senso-motor centers." ' Each one 
of the association areas is apparently devoted to estabUshing con- 
nections between the senso-motor areas which it adjoins. This is 
indicated in the following statement with regard to the functions of 
each of these areas: "The specific functions of the three association 
fields are determined in large part at least by their position with refer- 
ence to the senso-motor areas. The middle association field (island 
of Reil), situated as it is between the auditory area and that part of 
the somaesthetic area which receives sensations from the lips, tongue, 
throat, etc., is chiefly the association center for speech. The anterior 
and posterior fields have much more complex relations and functions. 
The posterior field, situated between the somaesthetic, visual, and 
auditory areas, receives from those areas impressions concerning the 
external world. The functions of this field arc to construct external 
objects from the several kinds of sense impressions and to form ideas 
concerning the relations of objects and physical processes to one 
another and to the self. In a word, the objective relations of the in- 

> O/*. «■/., pp. 345-346. ' 0/>. a/., pp. 349-351. * 0/>. «■/., p. 352. 



5oiri^^-5i^:^^i^^.^4^ea 



Parietal asso- 
ciation center 




Frontal association 
center 



Occipito-temporal 
association center 

Auditory Area 

Fig. II. — Diagram of the convex surface of the cerebral hemisphere. (After Morris.) 



Somaesthetic Area 



Frontal 
association ^ 
center 



Parietal asso- 
ciation center 
/ 




Occipito-temporal 
association center 



Olfactory Area 
Fig. 12. — Diagram of the medial surface of the cerebral hemisphere. (After Morris.) 



Cerebral Localization 183 

dividual and all those processes which we commonly call 'intellectuaP 
are the pecuhar province of the great posterior association field. . . . 
The anterior association field Hes in proximity to the somaesthetic 
area, but removed from the other sensory areas. It would receive in 
common with the posterior area the impressions due to contact with 
external objects and to the movements of the body, limbs, organs 
of speech, etc. Although the distant connections of the frontal lobe 
are not well understood, it seems clear that fibers from the visual 
and auditory areas are of subordinate importance, while association 
bundles from the olfactory (and gustatory) centers are next in im- 
portance to those from the somaesthetic areas." ^ 

Santee ^ gives a description of the cortical areas which is 
similar to that of Johnston, though the terminology used is 
somewhat different. He prefaces the description with this 
general statement. *'By repeated observation of the symp- 
toms produced by definite brain lesions and by the anatomi- 
cal and physiological study of human and lower animal 
brains, both in the embryonic and adult condition, the 
cortex has been mapped out into certain definite functional 
areas. Psychic function undoubtedly is dependent upon 
the associated activity of a number of cortical areas ; but 
motor, common sensory, and special sensory regions have 
been outlined with considerable, exactness." 

The motor area he locates as follows: "The emissive motor 
area is situated in the anterior wall of the central sulcus, in the pos- 
terior one-half of the gyrus centralis anterior and in that part of the 
paracentral lobule immediately continuous with it. This is the 
center for ordinary voluntary motion on the opposite side of the body. 
Axones from this area descend to the nuclei of all motor nerves." 
This area is divided into four segments ; namely, the head and neck, 
the arm, the trunk, and the leg. He then describes the psychic 
motor areas: ^^The psychic motor areas, or areas for educated move- 
ments, are located just anterior to the above motor areas, in the an- 

1 Op. cit., pp. 354-355- * Op. cit., pp. 177-183. 



184 The Science of Human Behavior 

terior central gyrus and in the contiguous ends of the superior, middle, 
and inferior frontal gyri. These areas are beHeved to send their 
axones to the emissive motor centers in the cortex." These psychic 
motor areas include centers for the lower extremity, the arm, which 
is the writing center, and the organs for the voice, which is the motor 
speech center. The common sensory area is described as follows : 
"According to Dr. Alfred W. Campbell, the receptive area of common 
sensation is limited to the posterior wall of the sulcus centrahs, in- 
cluding the anterior one-half of the posterior central gyrus and that 
part of the paracentral lobule which is continuous with it." This 
area "is probably divided into segments similar to those of the motor 
area." He then locates the psychic sensory area. "A large portion 
of the remainder of the parietal cortex probably constitutes a num- 
ber of centers for the interpretation of common sensory impulses, 
hence the term, psychic sensory area." The divisions of this area 
are not known with certainty, but different investigators have believed 
that they have located the muscular sense and the parts that interpret 
tactile, pain, and temperature impulses. 

The sense of hearing he locates as follows: "The receptive acous- 
tic center is located in the transverse gyri and in that part of the 
superior temporal gyrus which is continuous with them." The 
psychic acoustic center is adjacent. The sense of vision is located 
as follows: "In the cuneus and Hngual gyrus is located the recep- 
tive optic center for the temporal half of the same retina and the nasal 
half of the opposite one ; perhaps, also, for the macula lutea of both 
sides." The psychic optic center is near to the receptive one. The 
senses of smell and of taste are located as follows: "The uncus 
hippocampi forms the chief cortical center oj smell, close to which in 
the fusiform gyrus is probably the gustatory center (Mills)." 

Some of the anatomical characteristics which difTerentiate these 
areas are indicated in the following passage: "The olfactory, au- 
ditory, visual, common sensory, and motor areas are all distinguished 
by a definite characteristic histological structure peculiar to each 
region (Campbell). MeduUation of the fibers in these cortical areas 
occurs at different times; and, according to Flechsig, in the follow- 
ing order: olfactory, tactile and muscular sense, visual, auditory, 
and gustatory." Certain other centers have been located, at least 
tentatively, such as the center of intonation, the naming center, the 
center of equilibration, and the center of orientation. As has already 



Cerebral Localization 185 

been suggested, not all of the centers which have been mentioned have 
been located with certainty, but further anatomical research aided by 
the other methods of investigation will undoubtedly increase greatly 
the number which are known with certainty. These cortical areas 
are connected with the receptor and effector organs for which they 
function by the projection fibers which we have already described. 
"All the above motor, somaesthetic, and special sense areas are pro- 
vided with projection fibers which connect them with definite muscle 
groups and surface regions and with the organs of special sense. 
Large parts of the cerebral cortex possess no projection fibers ; they 
are beheved to be associative in function." 

Next he describes the three association areas beginning with the 
anterior: "According to Flechsig, that part of the frontal cortex 
which is anterior to the motor region determines the temperament 
and individuaHty of the person ; and, as Mills declares, is the center 
of inhibition, self-control, attention, concentration, volition. It is 
the center of 'the abstract concept.' J. S. Bolton says of this associa- 
tion center that 'it is the last part of the cerebnun to be developed, 
and is the first to undergo dissolution ; it is underdeveloped in amentia 
of all grades and atrophied in dementia, according to its degree.' 
*It possesses the highest (mental) function' {Brain, Vol. XXIX). The 
posterior association center, composed of those portions of cortex situ- 
ated between the sensory region of the equatorial zone, in front, and 
the visual cortex of the occipital lobe, behind, determines the intel- 
lectuaHty of the individual. To acquire knowledge of the external 
world is thus the function of the posterior association center. Mills 
calls it the center of 'the concrete concept.' It includes three psychic 
areas — the common sensory, auditory, and visual. Flechsig regards 
the island (of Reil) as the middle association center. Lesions in it 
are associated with paraphasia." 

These association areas must have many fibers which connect 
them with sensory and motor centers. These fibers are described 
as follows: "They are situated within or beneath the cortex, the 
various parts of which they serve to unite. Association fibers become 
meduUated and actively functional only as mental effort and educa- 
tion gradually develop them. So far as the brain is concerned, edu- 
cation consists, first, in the development of the functional centers of 
the brain ; and, second, in the establishment of fines of rapid communi- 
cation between them. The short association fibers are the more 



186 The Science of Human Behavior 

numerous and are very important. They unite contiguous parts 
of the same gyrus and associate together adjacent gyri." ^ The num- 
ber of these fibers and the connections they estabUsh are indicated. 
"The short association fibers are almost infinite in their connections. 
They connect the receptive and psychic sensory areas, and their 
interruption on the left side causes inabiHty to interpret the sensa- 
tions, called mind-blindness, mind-deafness, stereognosis, etc. Again, 
those short fibers also associate the psychic with the psychic-motor, 
and the psychic-motor with the emissive-motor centers. In this 
manner the writing center is connected with the motor center for the 
upper extremity, and the speech center with the motor centers for 
the Hps, tongue, etc. : breaking of the former connection on the left 
side destroys ability to write, agraphia; and aphasia results, if the 
latter connection is broken. Besides these and many other connec- 
tions of associated centers, the short fibers join together the various 
parts of each cortical area." ^ 

Before leaving the subject of the anatomical study of 
cerebral locaHzation we must touch upon the subject of 
the neural connections of these cerebral centers with their 
receptor and effector organs. 

Santee has discussed this subject well in his chapter on the "Trac- 
ing of Impulses. " ^ He classifies the neural paths by which these 
connections are estabHshed as follows: "I. Efferent, or motor. II. 
Afferent, or sensory — general and special sense. III. Reflex." 
These paths are direct when they do not pass through the cerebellum, 
and indirect when they do pass through it. The cerebellum, then, 
performs the function which we have already discussed and which is 
indicated in the following citation : "The cerebellum is an important 
relay in the indirect motor and indirect sensory paths. In response 
to impulses received from skin, muscles, tendons, joints, and viscera, 
it is also believed to originate impulses which coordinate muscles 
and maintain equilibrium. Moreover, according to Russell, each 
cerebellar hemisphere exercises an important inhibitory function, 
through the brachia conjunctiva, upon the opposite side of the 
cerebrum." * 

1 Op. cit., p. 236. * Op. cit., pp. 237-238, • Op. cit., chap. VII. 

* Op. cit., p. 242. 



Cerebral Localization 187 

I have not the space to discuss at length these paths, but will indi- 
cate the two types of sensory paths, namely, the general and special. 
"The sensory paths conduct two varieties of impulses, viz., general 
and special. The impulses originate in the end-organs of the cerebral 
and spinal nerves, and by those nerves are conveyed to the cerebro- 
spinal axis, through which they reach the proper cortical area in the 
cerebrum." The general sensory paths perform the following func- 
tions: "General sensation is the function of the sense of touch. 
This sense hei,sfour important subdivisions — the tactile sense, muscu- 
lar sense, pain sense, and temperature sense. Stereognosis is only an 
associated interpretation of all the impulses of the sense of touch, and 
not a subdivision of it. Tactile sensations appear to be most ele- 
mental and, according to Mills, may be conducted by all common 
sensory nerve fibers. Other common sensations seem to require 
some specialization, as yet not understood, in their conducting media ; 
and pain and temperature impulses pursue a path entirely distinct 
from that followed by impressions of the muscular sense. ^^ The special 
senses are those of smell, sight, hearing, and taste. "Impulses pro- 
ducing the sensations of smell, sight, hearing, and taste are carried 
from the respective organs of sense to the brain by the following 
nerves : the olfactory, the optic, the auditory, and the glossopha- 
ryngeal and intermediate nerves." 

The reflex paths Santee classifies as follows: "Reflex arcs are 
formed : (i) by the sensory and motor fibers of spinal nerves, asso- 
ciated in the gray matter of the cord; (2) by the sersory and motor 
fibers of cerebral nerves, which are connected in the brain; (3) by 
afferent spinal fibers connected by the ascending fibers of the medial 
longitudinal bundle, with efferent cerebral fibers ; and (4) by afferent 
cerebral and efferent spinal nerve fibers, the two being associated by 
the anterior longitudinal bundle, the ponto-spinal tracts, the fasciculi 
proprii, the spinal tract of the fifth nerve, the vestibulo-spinal tract, 
the solitary tract, etc." These classes of reflexes he calls (i) spinal 
reflexes, (2) cerebral reflexes, (3) spino-cerebral reflexes, (4) cerebro- 
spinal reflexes. 

The preceding has been a brief discussion, based in the 
main on writings of two authorities, of the anatomical 
researches with regard to cerebral locaKzation. Before 
leaving the subject we must touch upon the physiological 



188 The Science of Human Behavior 

and clinico-pathological investigations of the same subject. 
These two lines of investigation are closely related to each 
other. For that matter, these two are also closely related 
to the anatomical method of research. The results attained 
along each Kne throw light upon the results attained along 
the other lines, so that it is impossible to separate the 
three from each other to any great extent. 

Physiological Study of Cerebral Localization 

As has aheady been indicated, in the physiological study 
of cerebral localization two methods of research are used ; 
namely, stimulation and extirpation. Electricity is fre- 
quently used in stimulating the cerebrum. It is evident 
that if upon stimulating a certain part of the cerebrum a 
motor reaction follows, it is reasonable to suppose that this 
motor function is localized in this part of the cerebrum. 
In similar fashion a deduction may be made from the re- 
sponse to any stimulation as to the function which is local- 
ized in that part of the cerebrum. It is, however, well to 
check the results from this line of investigation by means of 
other methods of research. By extirpating a part of the 
cerebrum and observing what functions disappear, we can 
determine tentatively what functions are localized in that 
part of the cerebrum. As has already been indicated, 
however, there is always some uncertainty in such a deduc- 
tion. In the first place, the surgical shock from the opera- 
tion may have affected other parts of the cerebrum in such 
a way as to prevent them from functioning, so that more 
functions disappear than can be attributed to the part 
which has been extirpated. In the second place, other 
parts of the cerebrum may compensate for the part which 



Cerebral Localization 189 

has been extirpated, so that the functions localized in that 
part may not disappear. That is to say, these functions 
may be taken up by other parts of the cerebrum, so that 
it will not be apparent what functions were localized in 
the part which has been extirpated. Such compensation 
can take place only when a function is not absolutely local- 
ized in one part of the cerebrum, but may be performed by 
other parts as well. It is evident, therefore, that in the 
case of extirpation, also, the results of this line of investiga- 
tion should be checked by researches along other lines as 
well. The extirpation method is especially valuable for 
the study of the parts of the cerebrum which are not ex- 
citable, or, rather, which do not display noticeable ejffects 
upon stimulation. 

CHnico-pathological investigations have thrown much 
light upon cerebral locaHzation. Where there has been 
derangement in the behavior of an individual it has some- 
times been possible by means of trephining operations in the 
living and by means of autopsies in the dead to locate the 
lesion which was the cause of the derangement. Thus 
conclusions could be arrived at as to the localization of the 
functions which have been deranged. This method of 
investigation has peculiar value for the study of cerebral 
locaHzation in man. Frequently the patient can give 
detailed information as to the nature of the derangement, 
which is of great value, especially in the study of localization 
in the association areas. 

Let us note a few illustrations of these methods of investigation. 
Franz, who has been one of the leading investigators of the frontal 
lobes of the cerebrum, gives as follows the results from some of his 
stimulation and extirpation experiments, though he has used material 
from pathological cases as well ; — 



190 The Science of Human Behavior 

''A. In monkeys and cats the frontal lobes are normally employed 
in the formation of simple associations. 

"B. When the frontal lobes are destroyed, recently formed habits 
are lost. 

"C. The loss of the associations is not brought about by lesions 
of other portions of the brain. 

"Z). The loss of the associations is not due to shock, for lesions 
of other parts of the brain are not followed by loss of habit, nor does 
the anaesthetic and loss of blood, etc., produce loss of associations. 

"E. Unilateral lesions of the frontal areas are not followed by a 
loss, but there may be a slowing or retardation of the motor response. 

"F. Habits once lost after removal of the frontal s may be relearned. 
The relearning takes about as long a time as if the animal were 
learning a new association. 

"G. Only newly formed habits seemed to be lost after such lesions. 
Long-standing habits seemed to be retained. 

"H. The emotional condition of the animal remains the same after 
as before the removal of the frontals." ^ 

From these results he draws the following conclusions: "From 
the clinical and experimental results of others as well as those which 
have been recorded in the present paper I conclude that the frontal 
lobes are concerned in normal and daily associational processes and 
that through them we are enabled to form habits and, in general, 
to learn." ^ 

In a later writing on the same subject Franz gives the following 
summary of the knowledge as to functional localization in the brain : 
"Although the consideration of the known functions of the cortical 
areas has been necessarily brief, sufficient indication has been given 
that the motor and the sensory (hearing, touch, vision) cortical mecha- 
nisms are understood and localized. Opposed to this definiteness 
there is a vagueness in regard to the functions of the association areas. 
Some few facts are known, but there appears to be more or less haze 
about the subject, and writers tend to avoid it. Following is a sum- 
mary of the known facts regarding the two large association areas: 
(a) in the frontal association area are located centers of motor speech 
and writing ; (b) in the posterior association area are centers for what 
clinicians call the understanding of auditory and visual speech; (c) 

1 S. I. Franz, On the Functions of the Cerebrum: The Frontal Lobes, in the Archives 
of Psychology, Vol. I, New York, 1908, p. 63. ' Op. cil., p. 64. 



Cerebral Localization 191 

the frontal regions are clearly associated with the production of move- 
ments, especially those of a complex character; (d) in the posterior 
association area (or in the closely associated intermediate postcentral 
cortex) is an area for the understanding, through the medium of 
the skin and motor sensations, of the character of objects; {e) the 
results of my work on monkeys and cats indicate that both the frontal 
and the posterior association areas are concerned in the formation 
of simple sensori-motor habits." ^ 

Later on he indicates the special functions of the frontal portions 
of the cerebrum. "Evidence is at hand to show that the frontal 
areas have a more direct connection with the motor areas than do 
the posterior. The variations of reflex movements concomitantly 
with variations in frontal lobe activity have been mentioned. ... It 
is by a continual process of adjustment that man has attained his 
place in the world, and the varieties of activities so characteristic of 
him is made possible through the frontal regions. The direct motor 
responses of an animal need no large amount of association elements, 
but the indirect reactions of man require an amount of coordination 
that is supplied by the association cells. There is the increased use 
of the hands, of tools, of the legs, and of other mechanisms for pro- 
pulsion, requiring new adjustments and new associations; and the 
impulses to act are paralleled by a similar number of impulses to check 
activity, or tending to check the primary, reflex-like impulses." ^ 
Then he indicates the special functions of the posterior portions of 
the cerebrum. "The posterior areas are, from the accounts given 
above, clearly more closely allied with the sensory spheres. The 
large size of this region in intellectual men is only one indication of 
this, but the sensory aphasias and other similar processes that are 
located here by clinicians confirm this view." ^ 

Clinico-pathological Study of Cerebral Localization 

As has already been indicated, the clinico-pathological 
and the physiological methods of investigating cerebral 
localization are closely related. As a matter of fact, a 

1 S. I. Franz, On the Association Functions of the Cerebrum, in the Jour, of Phil. 
Psych, and Sci. Meth., Vol. VII, No. 25 (Dec. 8, 1910), p. 679. 

2 Op. cit., p. 681. 8 Op. cit., p. 681. 



192 The Science of Human Behavior 

pathological lesion and an experimental extirpation may 
have the same effect, because in each case a certain part of 
the cerebrum has been destroyed or has been cut off from 
the rest of the nervous system so that it can no longer per- 
form its function. In other words, the experimenter has 
done intentionally what disease or accident may do quite 
unintentionally. A vast number of data have been gathered 
with regard to the relations between pathological mental 
conditions and forms of behavior and abnormal conditions 
of the brain. 

The significance of these data for cerebral localization is well 
stated by Johnston in the following passage: "Thus, in case of any 
disease or injury which produces a lesion of a part of the cerebral 
cortex, one or more bodily functions may be interfered with, and the 
study of many cases has shown clearly that the functions affected 
depend upon the specific regions of the cortex injured. A sufficient 
number of facts of this sort have been collected from cUnical observa- 
tions, post-mortem examinations, and surgical operations to render 
fairly certain and accurate the determination of the area of the cortex 
involved in case of a brain tumor, degeneration of a cortical substance, 
or other cause of disturbance. If the patient shows symptoms of 
disturbance in the functions of sight, hearing, bodily sensation, or 
voluntary movement including speech, certain specific areas of the 
cerebral cortex may be pointed out as the seat of the disease, and in 
the case of bodily sensation or movement certain subdivisions of the 
cortical area may be assigned to certain parts of the body." ^ 

Santee indicates in the following passage the different results from 
lesions, on the one hand, of the motor or sensory cortex, and, on the 
other hand, of the association centers: '^Destructive lesions of parts 
of the motor or sensory cortex cause merely loss of certain motions 
and sensations represented by those parts, but ablation of association 
centers disconnects the sensory, the psychic, and the motor regions 
and causes aphasia, agraphia, change of temperament, impairment of 
the so-called moral and intellectual faculties, etc. Ablation of the 

1 Op. cit., pp. 343-344. 



Cerebral Localization 193 

visual psychic center or auditory psychic center produces mind-blind- 
ness in the former and in the latter mind-deafness." * 

Bolton describes how the cerebral cortex evolved from three 
primary cell laminae or layers, and shows how pathological conditions 
arise from the sub-evolution or degeneration of these laminae. "In 
cases of mental disease grading from idiots and imbeciles through 
various types of non-demented and partially demented lunatics to 
the gross dement, great differences in the degree of evolution and 
dissolution of the cortex exist; and these, considered from the gen- 
eral aspect, follow the order of normal development. In amentia 
the condition is one of sub-evolution to different degrees, and in de- 
mentia the laminae suffer in the reverse order to that of their evolu- 
tion, the most affected being the latest developed, and the least affected 
being the earUest developed." ^ He goes on to indicate how the causes 
of these pathological conditions are locaHzed in the cerebral cortex. 
"The degree and type of these differences vary according to the region 
of the cortex, whether this be a projection area, a zone of special 
association, or the prefrontal (higher associative) region. In the 
case of the visuo-sensory area, the prominent features are poor evolu- 
tion of the pyramidal and polymorphic laminae and specialization 
of the granule or receptive lamina. There also exist individual varia- 
tions in the degree of evolution of the granule or receptive lamina, 
and in that of the pyramidal or associative lamina, which individual 
variations bear no relationship to the degrees of amentia or dementia, 
which exist in individual cases. In the case of the visuo-psychic 
zone, the important feature, apart from an especially good evolution 
of the granule or receptive lamina, is a marked degree of individual ■ 
variation with regard to the depth of the pyramidal or associative 
lamina. This individual variation is independent not only of the 
existing grade of amentia or dementia, but also of the individual varia- 
tion in this lamina which occurs in the visuo-sensory area." ^ At the 
end of this monograph he emphasizes the need for the study of these 
cases in order to determine the causal relations between these patho- 
logical conditions and the cerebral areas. "I, therefore, trust that 
the definite relationship, which exists between the chnical evidences 

1 Op. cU., p. 183. 

2 J. S. Bolton, A Contribution to the Localization of Cerebral Function, Based on 
the Clinico-Pathological Study of Mental Disease, in Brain, Vol. XXXIII, Part 129 
(1910), p. 105. 3 Op. cit., p. 105. 

o 



194 The Science of Human Behavior 

of amentia and dementia during life and the corresponding indications 
of cerebral sub-evolution and dissolution which are found after death, 
will in the future receive fuller recognition than has hitherto been 
bestowed upon it. The preliminary acceptance of this general truth, 
followed by the combined clinical investigation of individual cases 
and macroscopic and microscopic study of the cerebra of these, is, 
I am convinced, essential as a scientific basis for the rational study 
of mental disease." ^ 

But while many brain diseases can be localized in the 
cerebrum, there are other diseases which are caused by a 
general abnormal or pathological condition of the brain. 
Krafft-Ebing calls these diseases psychic or mental diseases. 
^' There can be no doubt that the disturbances of psychic 
functions as they occur in insanity are the expression of 
changes in the organ that, under normal conditions, makes 
possible the occurrence of the psychic processes. Thus, 
the psychic disease proves the existence of a disease of the 
cerebral cortex; and, since circumscribed cortical disease 
(focal lesions) can occasion only symptoms of defect refer- 
able to the diseased portion of the cortex, the psychic ab- 
normality can only be conditioned by a diffuse change in 
the cerebral cortex.'' ^ These diffuse changes he attributes 
in large part, if not wholly, to disturbances of nutrition. It 
may, however, be questioned if it is correct to limit the term 
psychic or mental disease to those diseases which are caused 
by a general pathological or abnormal condition of the 
cerebrum. There certainly are other diseases whose causes 
are in part or wholly localized which may be termed psychic 
or mental diseases as much as those whose causes are not 
localized. 

• op. cit., p. 131. 

' R. von Krafft-Ebing, Textbook of Insanity, Philadelphia, 1905, pp. 20-21. 



Cerebral Localization 195 

This distinction is the same as that which is frequently 
made between the so-called functional and the organic 
diseases of the brain. Many of those who make this dis- 
tinction are persons who are using pseudo-scientific and more 
or less unscientific methods for the cure of these functional 
diseases. These diseases are supposed to be caused in some 
mysterious way without any anatomical changes taking 
place in the brain, and they are supposed to be cured quite 
as mysteriously by methods which are not said to have any 
anatomical effect upon the brain. It cannot be emphasized 
too strongly that the functional as well as the organic 
diseases have an anatomical basis and that they differ from 
each other only in that the changes are not so great and are 
much more numerous and more widely distributed in the 
case of functional diseases. Krafft-Ebing makes this 
distinction between functional and organic diseases, and 
yet he seems to recognize their likeness. "Like many 
other diseases of the central nervous system without 
demonstrable post-mortem lesions, the majority of psy- 
chic diseases seem to be for that reason functional; 
to be the result of molecular changes — a disturbance of 
nutrition. The conception of many psychoses as being 
functional diseases must not, however, be given too wide 
an appHcation, and thus encourage neglect of investigation 
of the pathologico-anatomic foundation of the psychoses. 
It must not be forgotten that in many forms of mental 
disease pathologico-anatomic lesions are found which are 
almost identical." ^ And again he speaks as if functional 
diseases have an anatomical basis. **Thus, from an ana- 
tomic standpoint, mental disease may be defined as a diffuse 

1 Op. cit., p. 21. 



196 The Science of Human Behavior 

disease of the cerebral cortex consisting of changes which 
may vary from mere alterations of cortical nutrition to 
gross changes of structure, especially inflammatory and 
degenerative in character." ^ It would perhaps be better 
if the distinction between functional and organic diseases 
could be abandoned entirely, because in the last analysis 
all diseases are both functional and organic. 

1 Op, Cit., pp. 21-22. 



CHAPTER XI 

THE NATURE OF INSTINCT 

Mistaken conceptions of instinct, 197. — Instincts as congenital 
tendencies to action, 198. — The relation of instinct to tropism and 
reflex action, 198. — The adaptive nature of instincts, 205. — The 
structural basis of instincts, 206. — The hereditary nature of in- 
stincts, 208. — Instincts as characterizing species, 208. — The 
degree of permanency of instincts, 209. — Variations in instincts, 
209. — Reenforcement and inhibition, 210. — Combinations of 
instincts, 212. — The degree of perfection attained by instincts, 
213. — Instinct and consciousness, 214. — The relation between in- 
stincts and emotions, 220. — Definitions of instinct, 222. — An 
instinct as an inherited combination of reflexes, 226. 

In the discussion of the behavior of the lower organisms 
earlier in this book was described one important form of 
behavior, the tropism. In the description of the nervous 
system was described a second important form of behavior, 
the reflex action. We now come to a third important form 
of behavior, the instinct, or, more specifically, the instinc- 
tive action. 

The terms 'instinct" and "instinctive" are very fre- 
quently and usually mistakenly used. For example, in 
his most recent reading the present writer has noted the 
mention of humanitarian, prophetic, criminal, moral, re- 
ligious, patriotic, benevolent, and political instincts. And 
yet it is almost certain that not one of these instincts exists. 
In fact, the popular use of these terms merely implies more 
or less definite modes of action which are preceded by very 

197 



198 The Science of Human Behavior 

little or no deliberation. This is why instinct is frequently 
opposed to reason. Furthermore, it is frequently assumed 
that the behavior of animals is instinctive, while that of men 
is rational. It was generally believed in the past that the 
instincts were divine in their origin. For example, the Eng- 
lish writer Addison said that instinct is to be explained ''as 
an immediate impression from the first Mover, and the 
Divine energy acting in the creatures." ^ Presumably, 
in accordance with this theory, man has been divinely en- 
dowed with the higher faculty of reason. It goes without 
saying that this pious theory no longer has any standing 
in the Hght of modern science, and it is a grave error to Umit 
instinct to animals and reason to man. As a matter of 
fact, man shares most of the instincts with the animals, while 
some of the animals may possess a certain amount of reason. 
Let us therefore search for a more accurate conception of 
instinct. 

Relation of Instincts to Tropisms and Reflexes 

We may say, to begin with, that instincts are congenital 
tendencies to more or less definite modes of action. It is evi- 
dent that this definition would include tropisms and reflex 
actions, for, as we have seen, these forms of behavior are 
congenital and are more or less definite. And it is held by 
some writers on this subject that instincts are tropisms, while 
others believe that they are reflex actions. We shall there- 
fore have to consider these theories first before we can arrive 
at a more limited and detailed definition of instinct. 

Loeb, whom we have come to know as the great champion 
and exponent of the tropism theory, insists upon identifying 

* Quoted in G. J. Romanes, Animal Intelligence, 5th edit., London, 1892, p. n. 



The Nature of Instinct 199 

tropisms, reflexes, and instincts with each other. He con- 
tends that instincts consist largely if not entirely of tro- 
pisms, and that instincts cannot be distinguished from re- 
flexes. For example, he says: ^'It is evident that there 
is no sharp Kne of demarcation between reflexes and in- 
stincts. We find that authors prefer to speak of reflexes 
in cases where the reaction of single parts or organs of an 
animal to external stimuli is concerned ; while they speak 
of instincts where the reaction of the animal as a whole is 
involved (as is the case in tropisms)." ^ In similar fashion 
Folsom identifies these three forms of behavior with each 
other: ^'We have already emphasized that an instinct is 
a reflex act or a combination of reflex acts. The same 
fact may now be stated in these words : an instinct is a 
tropism or a combination of tropisms.''^ ^ T. H. Morgan 
seems to regard tropisms and instincts as identical. For 
example, he speaks as follows: '^Many of the so-called 
instincts of animals have been shown in recent years 
to be little more than direct responses to external agents." ^ 
He goes on to discuss as instincts various of these direct 
responses which are tropisms. 

It is evident that the first two of the three writers who 
have just been cited extend the idea of the reflex action 
to organisms without a nervous system. In an earlier 
chapter were discussed the reasons for restricting the use 
of this term to animals with a nervous system. Of the 
writers who do so and then identify instincts with reflex 
actions, the most distinguished is Herbert Spencer. In 

^ Comparative Physiology of the Brain, and Comparative Psychology, New York, 
1900, pp. 7-8. 

2 J. W. Folsom, Entomology, Philadelphia, 1906, p. 361. 
' Evolution and Adaptation, New York, 1903, p. 382. 



200 The Science of Human Behavior 

the first place, he defines reflex action as follows : *' Under 
its simplest form, Reflex Action is the sequence of a single 
contraction upon a single irritation," but *' Reflex Action 
proper is exhibited only when we ascend to creatures in 
which there exist nerves and muscles." ^ Then he defines 
instinct as follows: ^'Instinct may be described as com- 
pound reflex action." ^ He goes on to say that *'no clear 
fine of demarkation can be drawn between it and simple 
reflex action." 

After having written the preceding chapters, I hardly 
need to say that I beheve that there is strict continuity 
between all these different forms of behavior and that the 
more complex forms are built up from and based upon the 
simpler. The question, therefore, of what meanings we are 
to give to these terms is purely a matter of terminology, to 
be determined by considerations of expediency. In an 
earlier chapter I have stated my reasons for thinking that 
it is preferable to restrict the word reflex to the actions of 
animals with a nervous system. It is evident that if we 
extended the term to the actions of all animals, we should 
be calling all forms of behavior reflex, and in that case it 
would mean no more than to say that all forms of behavior 
are mechanically determined, in which case it would have 
little utiHty. For similar reasons it is, I believe, better not 
to identify instinct with tropism, for if we did so we should 
be giving to the word instinct a very broad meaning. In- 
deed, in the last analysis, it would then include every form 
of behavior, and consequently would have no utility in dis- 
tinguishing different forms of behavior. I shall therefore 
restrict the use of the term instinct to the behavior of ani- 

^ Principles of Psychology, Vol. I, New York, 1895, p. 427. ' Op. cit., p. 432. 



The Nature of Instinct 201 

mals with a nervous system. The next question is as to 
whether instinct is to be identified with reflex action. 

One group of writers have contended that instincts and 
reflex actions are to be distinguished from each other on the 
ground that an instinct involves a mental element, while a 
reflex action does not. Romanes is one of the best-known 
representatives of this group. He defines reflex action as 
follows: "This non-mental operation of the lower nerve 
centers in the production of apparently intentional move- 
ments is called Reflex Action." ^ Later on he states that 
instinct is reflex action with a mental element added. His 
definition of instinct is as follows: "Instinct is reflex 
action into which there is imported the element of conscious- 
ness." ^ I shall discuss the question as to whether or not 
an instinct necessarily involves consciousness further on 
in this chapter, while the whole subject of consciousness 
will be discussed more or less fully in a later chapter. The 
conclusion which will then be reached wifl be that instinct 
does not necessarily involve consciousness, so that this 
cannot be regarded as a distinguishing mark between re- 
flex action and instinct. 

Is there, then, any other distinguishing mark between 
reflex action and instinct? It seems quite evident that 
it is the tendency of neurologists to-day to regard all action 
which is determined by the nervous system as reflex. 
Practically all the actions of the higher animals are deter- 
mined by the nervous system. Certainly this is true of 
all actions which have an outward manifestation, while 
very few if any actions inside the body are not determined 
by the nervous system. A possible exception may exist 

* Animal Intelligence, London, 1892, p. 3. * OP' cit., p. 17. 



202 The Science of Human Behavior 

in the case of the muscles of the heart, which seem to be in- 
dependent of the nervous system sometimes, as in the 
embryo before the nervous system develops.^ This may 
also be true of the visceral muscles.^ It is evident that in 
accordance with this conception of reflex action all in- 
stinctive action must also be reflex, for all instinctive 
actions involve the nervous system. Upon accepting this 
conception of reflex action, the only distinction which can 
be made, if any can be made, between reflex action and in- 
! stinct is that an instinct involves more than one reflex 
action. This is in accordance with Spencer's definition of 
instinct as compound reflex action. According to this con- 
ception of instinct, then, any form of behavior which in- 
volves more than one reflex action is instinctive. Some 
writers, however, such as Lloyd Morgan,^ contend that for 
behavior to be instinctive it must involve the organism as 
a whole. If this be true, more than two reflexes would as 
a rule, if not always, be required to constitute instinctive 
behavior, for it is doubtful if any two reflexes alone would 
involve the organism as a whole. To the above might be 
added the statement, which so far as I know has not been 
made by any other writer on this subject, though many may 
have intended to imply it, that instinctive action is a 
form of behavior which has an outward manifestation, for 
there is probably no one who would call an internal pro- 
cess instinctive. 

If, then, the above considerations are correct, the only 
difference between a reflex and an instinctive action is 

» Cf. G. H. Parker, op. cit., p. 330; C. S. Sherrington, The Rdle of Reflex Inhibi- 
tion, in Science Progress, No. 20 (April 191 1), p. 585. 

2 Cf. W. H. Howell, Textbook of Physiology, Philadelphia, 1906, pp. 53-54- 
• Habit and Instinct, London, 1896, pp. 7, 27. 



The Nature of Instinct 203 

one of degree. An instinct would simply be a compound 
or complex of reflexes. There might still be difference of 
opinion, however, as to the degree of complexity needed 
to constitute an instinct. For example, some writers call 
the sucking action of the lips displayed by newly born in- 
fants an instinct. But Lloyd Morgan and the others who 
contend that instinctive action must involve the behavior 
of the organism as a whole could not regard this sucking 
action as being more than a reflex, for it does not involve 
the whole organism. 

Some writers, however, who have admitted that an in- 
stinct is made up of reflexes have still contended that there 
is a fundamental difference between an instinct and a re- 
flex. For example, Hobhouse has taken this position. 
He attempts first to distinguish between the two in this 
fashion: "Each particular act may be described without 
obvious violence as reflex, but the whole is an adaptive 
combination of reflexes in which the combination is as 
important as each separate act." ^ It is not, however, 
clear how this constitutes an absolute distinction between 
the two. Certainly, so far as adaptation is concerned, there 
can be no such distinction, for reflexes may be quite as 
adaptive as instincts. Instincts, therefore, still remain com- 
pounds or complexes of reflexes. He passes on, however, 
to a further distinction. After describing the instinctive 
fashion in which a hen cares for her chicks, and insisting 
that this is not reflex, he says: "There seems to be at 
least some permanent state corresponding to what we call 
maternal feeling, or the parental instinct which dominates 
the hen's actions throughout, and without which the various 

1 Mind in Evolution, London, igoi, p. 53. 



204 The Science of Human Behavior 

reflexes would not be discharged by their appropriate 
stimuli." ^ This passage seems to indicate that he thinks 
that an instinct involves a state of feeling, and that this 
is what distinguishes it from a reflex action. Apparently, 
therefore, his conception of an instinct is like that of Ro- 
manes, which has been discussed. 

A little further on he characterizes instinct again as fol- 
lows: "Where there is by heredity a certain setting de- 
termining reflexes in a special way, there is an instinct 
which is distinguishable from a compound reflex. The in- 
stinctive act is no longer one which follows with perfect 
uniformity from a certain stimulus. It follows from that 
stimulus only if it is appropriate to the setting of the or- 
ganism at the time. We have indeed already noted that 
reflexes may be adaptable to organic conditions. It is on 
such adaptable reflexes that instinct rests, and its business 
is precisely to shape them aright." ^ He himself recognizes 
in this passage that reflexes are adaptive, like instincts. So 
far as being hereditary is concerned, there can be no distinc- 
tion between the two. So that the only distinction ap- 
parently resides in this "setting," which he says determines 
the reflexes which constitute an instinct. Just what this 
setting is, he does not indicate, but it is presumably the 
state of feehng to which he has referred earlier but has not 
described. Hobhouse's description is therefore at best an 
ambiguous one, and his conception of an instinct seems to 
be like that of Romanes. As I have already indicated, this 
conception will be discussed later in this chapter. 

What, then, are we to say as to the relation between re- 
flex action and instinct? If we identify instinct entirely 

* op. cit., p. S3. > op. cit., p. 57. 



The Nature of Instinct 205 

with reflex action, the term would no longer have any utility 
in distinguishing different forms of behavior, for it would 
be synonymous with reflex action. Inasmuch as practi- 
cally all the actions of higher animals are determined by the 
nervous system, all the behavior of these animals is almost, 
if not entirely, reflex in its character. It is therefore im- 
possible to apply the term instinct to behavior which is not 
reflex. The only way of utihzing the term is therefore to 
apply it to a special group of reflex actions. I have already 
noted the distinguishing features of this special group. In 
the first place, they must be actions which have an out- 
ward manifestation. In the second place, there must be 
more than one of these reflex actions, and these actions must 
be so combined and related to each other that they will 
work towards a imifled end. That is to say, each must be 
adapted not only by itself, but also with relation to all 
the others. In other words, instincts appear in the course of 
the integration of the behavior of the organism which is 
effected by the nervous system and which has been de- 
scribed in an earher chapter. When we regard instinct in 
this fashion, the mystery and obscurity in which it has so 
frequently been shrouded at once disappears, and the nature 
of instinct becomes very simple and clear. 

Whether, then, we shall use the term depends upon the 
question as to whether it is worth while to give a special 
name to certain of the higher stages in this process of in- 
tegration. It is perhaps worth while to do so, because the 
use of this term emphasizes the part played by external, 
selective forces in guiding and, to a certain extent, determin- 
ing the course of this process of integration. It is a signifi- 
cant fact that neurologists very frequently do not use the 



206 The Science of Human Behavior 

word instinct even when discussing instinctive actions. For 
example, I doubt if Sherrington in his admirable account of 
the integrative action of the nervous system which has been 
cited uses the term instinct once, even though many of the 
integrated forms of reflex action which he describes are 
instinctive. And it is probably wise of these writers not 
to use the term, for by so doing they emphasize the reflex 
character of the behavior of the higher animals. But these 
scientists usually have all their attention centered on the 
nervous system of individual organisms and pay no atten- 
tion to the selective forces which are eliminating those 
organisms whose reflexes do not adapt them to their en- 
vironment, while they preserve those whose reflexes do so 
adapt them. The idea of adaptation is very closely as- 
sociated with the word instinct, and it may therefore be 
profitable to use the term in describing integrated reflex 
actions whose character has been determined in part by 
external selective forces. 

Having identified instinct with the forms of behavior 
of the whole organism which have been integrated by the 
nervous system, it is evident that in an earlier chapter, when 
discussing the integrative action of the nervous system, I 
was describing one aspect at least of the origin and evolu- 
tion of instincts. I shall, therefore, not repeat this de- 
scription, but will discuss briefly certain other aspects of the 
origin and evolution of instincts. 

Structural Basis of Instinct 

It must be evident by this time that instincts are based 
upon structure and that the relation between instincts and 
structure is the same as the relation between structure and 



The Nature of Instinct 207 

physiological activities. James apparently has this in 
mind when he says that instincts ''are the functional cor- 
relatives of structure." ^ Structure is therefore for in- 
stincts what the "action system" is for the behavior of 
the lower organisms, as we have seen in an earlier chap- 
ter. The origin and evolution of instincts is therefore 
analogous to that of structure. The fundamental prin- 
ciples of morphological evolution have been discussed in 
earlier chapters. We have seen that structural forms evolve 
either as the result of the accumulation of slight variations 
which are preserved because they have utility, or as the 
result of mutations of more or less size which appear in- 
dependent of utility and which therefore may or may not 
prove to be useful. If an instinct was determined by a 
structural form which had evolved as a result of the accumu- 
lation of sHght variations, it would probably make its appear- 
ance slowly and would be useful from the start. If, how- 
ever, an instinct was determined by a structural form which 
was the result of a sudden mutation, it also would probably 
appear suddenly and would not necessarily be useful at the 
start. So far as I know, no such sudden appearance of an 
instinct as the result of a mutation has been observed. But 
if it be true, as I have contended, that instinct is based 
upon structure, and if structural forms may result from 
sudden mutations, there is every reason for believing that 
instincts may appear in this sudden fashion. It may be 
contended by some that such new forms of behavior would 
not be instincts if they were not useful, for many writers 
have insisted upon the utility of instincts as an essential 
characteristic. But while in the long run instincts are cer- 

1 William James, Principles of Psychology, New York, 1896, Vol. II, p. 383. 



208 The Science of Human Behavior 

tain to be useful, for otherwise they would be eliminated, 
an instinct may not be useful at the start when it is the re- 
sult of a sudden mutation, and an instinct which has been 
useful may lose its utility. 

Characteristics of Instinct 

It must now be evident that instincts are hereditary 
just as the structures upon which they are based are heredi- 
tary. It has been contended by some that instincts origi- 
nate in modes of behavior acquired by the individual which 
are usually called habits, or in memories which may also be 
reduced to terms of habit which are inherited. It is evi- 
dent that we cannot accept this theory of the origin and the 
hereditary nature of instinct unless we accept the theory of 
the inheritance of acquired characters, and, as we have seen 
in a previous chapter, there is Httle ground for beheving 
this theory. 

The next question which arises is as to the number of 
individuals to which an instinct must belong. Some 
definitions of instinct state or imply that an instinct is a 
form of behavior which characterizes all or most of the 
members of a species. It is true that an instinct tends to 
become a specific character, because if it proves to have 
great utility, the individuals possessing it will be preserved, 
while those which do not possess it will be eHminated. But 
at its inception an instinct cannot very well belong to a 
whole species unless it in itself, or rather the structural 
form upon which it is based, marks the beginning of a new 
species. If an instinct is the result of a sudden mutation, 
it will at first belong to but one individual. Then it will 
be transmitted to the immediate descendants of this indi- 



The Nature of Instinct 209 

vidual, and if it proves to have great utility, it may become 
a specific character in the manner indicated above. 

It is thought by many that instincts are permanent and 
unchanging in their character. But it is evident that they 
can be no more permanent than the structural forms upon 
which they are based. We have seen that variations and 
mutations cause new instincts to come into existence. In 
similar fashion variations and mutations cause changes in 
instincts already in existence because they change the 
structural basis of these instincts. Sometimes these varia- 
tions and mutations cause instincts to disappear gradu- 
ally or suddenly. These changes in instincts are hereditary 
in their character. Are there any changes in the instinc- 
tive tendencies of the individual which are not hereditary 
in their character? If there are any such changes they 
must be due to structural changes which cannot be inherited. 
Let us see whether there are any such changes. 

A simple reflex action is not likely to be changed, because 
its structural basis is fairly simple, and changes in it are not 
likely to take place. But the structural basis for the tmified 
behavior of the whole organism which arises out of a group 
of reflexes which have been integrated together by the 
nervous system and which we call instinctive is much more 
complex, and the possibility of changes taking place in this 
structural basis is correspondingly greater. It is therefore 
in the nervous system by which this integration of reflexes 
has been effected that these changes in the structural basis 
usually take place. And the nervous system is so dehcate 
and so complex that changes in it which are very slight in 
bulk may have a great effect upon the behavior of the 
organism. These changes may, however, take place in other 



210 The Science of Human Behavior 

parts of the organism. For example, one of the most im- 
portant and permanent of the instincts is the sexual instinct. 
The structural basis of this instinct is to be found in part 
in the sexual organs and in part in the nervous system. 
If the operation of castration is performed in which the 
sexual organs are removed in part or entirely, the instinc- 
tive sexual tendency will disappear in part, if not entirely. 
If such a change is not observed, it must be due to the fact 
that a habit has become so firmly estabhshed on the in- 
stinctive foundation that it persists in its full strength 
even though the structural basis for the instinct has been 
in part removed. 

But let us see what changes appear in instinctive re- 
actions as a result of changes in the nervous system. As 
we have seen, an instinctive act is one that is performed 
without any previous training or experience the first time 
that the appropriate stimuli affect the organism. Conse- 
quently there can be no knowledge or foresight of the conse- 
quences of the act by the individual before the act is per- 
formed. This is why it is so unfortunate that instinctive 
actions are so frequently spoken of as purposive or teleo- 
logical in their character. They may be adaptive and there- 
fore useful, but inasmuch as in a purely instinctive act the 
individual does not foresee the consequences of the act, 
there can be no purpose on the part of the individual. 
The situation is changed, however, when the act is repeated, 
for then the factor of experience enters in to affect the be- 
havior. The individual now has a knowledge of the con- 
sequences of the act and will be influenced accordingly. 
If the consequences have been pleasant, the tendency to 
perform this act will be strengthened. If the consequences 



The Nature of Instinct 211 

have been unpleasant, the tendency to perform this act will 
be weakened and perhaps in course of time inhibited entirely. 
Thus it is that through associations estabhshed in the cen- 
tral nervous system instincts are reenforced or inhibited. 

Let us see what are the principal ways in which such 
reenforcement or inhibition takes place. As we have seen, 
an instinctive action is stimulated by any one of a group 
of objects which are more or less aHke and which starts off 
the series of reflexes which constitute the instinct. An 
instinctive action may be stimulated in an individual a 
number of times by the same one of this group of objects. 
Thus the habit of responding to this one object may be- 
come firmly established, so that when the individual is 
subjected to the stimulus of other objects of this group it 
will be prevented from responding to these because of the 
habit which has become estabhshed in favor of the first 
one.^ Thus the tendency to respond to the first object 
of the group will be greatly reenforced, while the tendency 
to respond to the other objects of the group will be inhibited. 
It is easy to see that such reenforcement and inhibition 
arise out of paths of association which have become estab- 
hshed in the central nervous system. 

An instinctive reaction may be stimulated by the image 
of one of the group of objects which ordinarily arouse it. 
The image of an object arises out of an association center 
or group of association centers which is necessarily con- 
nected with the sensory center which that object stimulates. 
If this association center or group of association centers 
is also connected with the motor center which governs the 
instinctive reaction, stimulation of this center or group of 

* Cf. W. James, op. cit., p. 394. 



212 The Science of Human Behavior 

centers may be sufl&cient to arouse the motor center. Thus 
an instinctive reaction may be aroused by the image of an 
object, even though the individual has not been subjected 
to the stimulus of the object itself. In similar fashion an 
instinctive reaction may be stimulated by another object, 
or the image of another object which is connected by paths 
of association with the object which ordinarily arouses the 
instinctive reaction, and also with the motor center which 
governs the instinctive reaction.^ The neural basis for 
the fact that the same instinctive action can be aroused 
by stimuH from several sensory and association centers is 
probably indicated in the principle of the common path 
which has been discussed in an earlier chapter. It will be 
recalled that this principle is to the effect that a final or 
efferent neurone is a pubhc path ''common to impulses 
arising at any of many sources of reception." 

The form of behavior which an instinctive reaction takes 
may vary greatly as the result of habit based upon expe- 
rience. This is peculiarly true of man, whose behavior is 
controlled to a certain extent by intelligence and is in- 
fluenced by imitation. Such variations in the form of be- 
havior manifested in an instinctive reaction are most Hkely 
to take place in the case of instincts which ripen slowly, 
so that intelligence has an opportunity to influence the 
form the instinctive reaction is to take.^ 

Different instinctive reactions may be stimulated at the 
same time and then inhibit each other in part or entirely, 
or they may be combined in forms of behavior in which 
each reaction becomes somewhat modified. 

^ Cf. W. McDougall, Introduction to Social Psychology, Boston, 1909, pp. 32-40. 
« Cf. McDougall, op. cit., pp. 40-43. 



The Nature of Instinct 213 

The individual variations in instinctive reactions which 
have just been briefly described are caused in large part or 
entirely by the establishment of paths of association in 
the brain which connect new centers with the motor centers 
for instinctive reactions. There is a certain type of in- 
stinct in which a lack of uniformity in the instinctive re- 
actions may seem to indicate individual variations. These 
are the transient instincts which appear temporarily. The 
appearance and disappearance of these instincts is, of course, 
due to changes in the structure of the individual. But in- 
asmuch as these changes are common to the whole group, 
which is characterized by a transient instinct, this group 
usually being a species, the variation in the instinctive re- 
action can hardly be spoken of as an individual variation. 

It is a popular idea that instincts are perfect. But the 
variations in instincts which have just been discussed in- 
dicate that very frequently, if not always, they are imperfect. 
This raises the question as to what constitutes perfection. 
It is hardly necessary to say that science does not recognize 
any absolute metaphysical or moral standard of perfection. 
If it recognizes any standard at all, it must be a relative one. 
In the organic world it is utiHty in the struggle for exist- 
ence. Thus instincts are perfect to the extent to which 
they are useful in the struggle for existence of the organ- 
isms which possess them. Can it be said, then, that in- 
stincts are ever perfect in accordance with this standard ? 
It is true that selection is always at work preserving the 
instinctive reactions which are useful and eliminating those 
which are injurious and, to a certain extent, those which are 
not useful. But selection has probably never succeeded 
in making an organ or an organic character as adaptive 



214 The Science of Human Behavior 

and therefore as useful as it might have been. Conse- 
quently every organ and organic character has fallen short 
of perfection according to our relative standard, and always 
there has been room for improvement. This is true even 
of so highly developed an organ as the human eye, as was 
shown by Helmholtz. It is therefore hardly conceivable 
that any instinct was ever perfect in the sense that it was 
perfectly adapted to the needs of the organism. Certainly 
it would be more difficult for an instinct to become per- 
fectly adapted than for most organic characters, because 
of the complexity of the series of reflexes which constitutes 
an instinctive reaction. Furthermore, even if an instinct 
did become approximately perfect, it would probably not 
remain so for very long, for the needs of the organism would 
be likely to change soon, thus necessitating changes in the 
instinctive reaction. Lloyd Morgan has indicated the 
character of instinct very well in the following statement : 
"Instinctive behavior is practically serviceable on the oc- 
casion of its first performance." ^ That is the truth about 
instinct, — it tends to be practically serviceable rather than 
theoretically perfect. 

Instinct and Consciousness 

We must now take up the question of the relation of in- 
stinct to consciousness. As has been noted, certain writers 
have contended and do now contend that an instinctive ac- 
tion always involves a mental element, and by this mental 
element they usually mean consciousness. This question, 
like so many others, depends to a large extent upon the way 

1 The British Journal of Psychology, Vol. Ill, Part 3 (October, 1910), p. 225. 
The italics are mine. 



The Nature of Instinct 215 

in which we define certain terms. If a sufficiently broad defi- 
nition is given to such words as mind and consciousness, no 
one would deny that an instinctive action always involves a 
mental or conscious element. Such would be the case if it 
were contended, as it is by spme, that mind or consciousness 
is the essential vital characteristic of all organisms. In that 
case a mental or conscious element would necessarily enter 
into every organic activity. But if we are to limit the 
meaning of these terms somewhat narrowly, we may be 
able to prove that a mental or conscious element is not 
necessarily present in every instinctive action. Let us note 
briefly some of the theories that contend that an instinct 
necessarily includes a mental or conscious element. 

I have already referred to Romanes' theory that an in- 
stinct always involves a mental element, while a reflex 
action does not, and that this mental element in instinct is 
consciousness. We must determine next what he means by 
consciousness. In his chapter ^ on this subject he refuses 
to define consciousness in what he believes to be its char- 
acter as a mental or psychic phenomenon, but he describes 
the physiological basis of consciousness. He contends that 
consciousness arises when there is enough delay between a 
stimulus and the response of the organism to it to permit of 
its appearance. In the case of a simple reflex he believes 
that the time is not long enough to permit consciousness to 
appear, but in the case of an instinctive action he beheves 
that there is time enough and that the consciousness always 
does appear. Before commenting on this conception of con- 
sciousness, I wish to speak of the other reasons which Ro- 
manes apparently has for insisting upon consciousness as an 

1 Mental Evolution in Animals, New York, 1898, chap. VI. 



216 The Science of Human Behavior 

essential part of instinct. Again and again in his extensive 
writings on instinct he speaks of instinct as hereditary 
memory. Furthermore, he classifies instincts as primary 
and secondary according to their modes of origin. Pri- 
mary instincts result from the natural selection of actions 
"which, although never in telKgent, yet happen to have been 
of benefit to the animals which first chanced to perform 
them." ^ Secondary instincts result from the hereditary 
transmission of habits of actions originally intelligent. 
George Henry Lewes considered these instincts cases of 
'' lapsed intelligence." It is evident that throughout 
this discussion Romanes is implying a beHef in the in- 
heritance of acquired characters, a theory of which he was 
an ardent supporter. Memory, according to the usual 
meaning of that term, is an acquired character, and Romanes 
seems to be using it in this sense. ^ While he does not ex- 
pressly say so, he seems to imply that the primary instincts 
result from habitual modes of action which have been ac- 
cidentally acquired and then preserved for hereditary trans- 
mission by natural selection. He states expHcitly that the 
secondary instincts result from the hereditary transmission 
of acquired habits. So that it is evident that his conception 
of instinct is based throughout upon the hypothesis that 
acquired characters are transmissible by heredity. He 
implies that the consciousness of their acts possessed by 
past generations is somehow transmitted so that even the 
first time an instinctive act is performed it is accompanied 

1 op. cit., p. 178. 

' "Hereditary memory, or instinct, belongs to what I have marked off as the 
second and third stages of conscious memory in the largest acceptation of the term 
— the stages, that is, where, without any association of ideas, a present sensation 
Is perceived as like or unlike a past one." — Op. cit., pp. 115-116. 



The Nature of Instinct 217 

by consciousness. As we have seen in an earlier chapter, 
there is very Httle reason for believing in the hereditary 
transmission of acquired characters, while practically all 
the evidence is against it. Consequently most of Romanes' 
reasons for thinking that instinct always involves conscious- 
ness fall to the ground at once. 

Returning to his conception of the nature of consciousness 
described above, let us see if that furnishes any ground for 
this belief. There can be httle question that some delay 
between stimulus and response is necessary for the appear- 
ance of consciousness. But it may be questioned whether 
this is the only requisite condition. I shall not discuss 
this question here, because it will be discussed more or less 
thoroughly in a later chapter. But even if a certain amount 
of delay between stimulus and response were the only 
requisite condition for consciousness, it is doubtful if the 
delay is long enough in the case of many instinctive actions 
to give rise to consciousness. The delay in an instinctive 
action which involves several reflexes is longer than in a 
simple reflex because it involves a more compHcated nervous 
adjustment. But even in an instinctive action the response 
is frequently very immediate, so that there is Httle chance 
for the appearance of consciousness. This is very hkely 
to be the case the first time an instinctive action takes place 
before any habits or other inhibiting forces have developed 
to delay the response. But this may be the case, also, when 
an instinctive act has been many times repeated, so that 
habits and other acquired characters reenforce it and lessen 
the time between stimulus and response. Consequently, 
even in accordance with the very simple criterion of con- 
sciousness which Romanes proposes, it may be questioned 



218 The Science of Human Behavior 

whether instinct always involves consciousness, while it 
becomes still more questionable in accordance with a more 
complex criterion, as, for example, the one which I shall 
outline in a later chapter. It seems quite evident, there- 
fore, that Romanes' reasons for beheving that consciousness 
is an essential element in instinct were very poor. 

It would take too long to discuss all the theories of in- 
stinct which have insisted upon a mental or psychic element 
as an essential part. I have already commented upon 
Hobhouse's theory, which seems to be similar to that of 
Romanes. In his recent discussion of instinct, which in 
many respects is most excellent, McDougall offers the fol- 
lowing definition of instinct: "We may, then, define 
an instinct as an inherited or innate psycho-physical dis- 
position which determines its possessor to perceive, and to 
pay attention to, objects of a certain class, to experience 
an emotional excitement of a particular quality upon per- 
ceiving such an object, and to act in regard to it in a par- 
ticular manner, or, at least, to experience an impulse to 
such action." ^ It is evident that this definition is heavily 
weighted with psychological impHcations ; much more so, 
in fact, than the great majority of definitions of instinct, 
and is, therefore, very different from the much simpler 
biological conception of instinct in which we are most 
interested. 

Let us see what these psychological impHcations are. 
In the first place, he says that an instinct is a "psycho- 
physical disposition." We have seen that very different 
meanings are given to such terms as "psychic," "mental," 
and "conscious." If it is contended that all organic matter 

' Op. cil., p. 29. 



The Nature of Instinct 219 

possesses psychic quaKties, then it is easy to beUeve that 
an instinct is in part at least psychic. If, however, we are 
to limit the meaning of the term more narrowly, an instinct 
may not always be psychic. We must therefore determine 
how complex are the ''psychic" characteristics which Mc- 
Dougall attributes to instinct. He says that ''there is 
every reason to believe that even the most purely instinctive 
action is the outcome of a distinctly mental process," and 
that it "can only be fully described in terms of the three 
aspects of all mental process — the cognitive, the affective, 
and the conative aspects ; that is to say, every instance of 
instinctive behavior involves a knowing of some thing or 
object, a feeling in regard to it, and a striving towards or 
away from that object." ^ It is evident that he beHeves 
that even the simpler instinctive actions involve such highly 
developed mental phenomena as knowledge, a complex 
feeling in the form of an emotion, and conscious effort to- 
wards an end. But the preceding discussion certainly has 
been sufficient to show that instinctive actions, which are 
series of reflexes which have been integrated by the central 
nervous system, appeared long before any one of these 
mental phenomena had developed, so that no one of these is 
an essential part of an instinct. If, then, any psychic phe- 
nomena are always involved in instinctive actions, they must 
be more simple than the ones enumerated by McDougall. 
As has been indicated, my own conception of the psychic is 
to be outhned in a later chapter. All I need to say here is 
that I beHeve that psychic phenomena arise out of the ad- 
justments accomplished by the central nervous system 
in the interval between the reception of a stimulus by a 

* Op. cit.y p. 26. 



220 The Science of Human Behavior 

sense organ and the sending of an impulse to a motor organ. 
But these adjustments must be relatively complex to give 
rise to such psychic phenomena, and it is almost if not 
quite certain that the adjustments involved in many of 
the simpler instinctive actions, like those of the simple re- 
flexes, are not sufficiently complex to give rise to psychic 
phenomena. 

To continue this discussion of the psychological implica- 
tions in McDougall's definition, we may note in the second 
place that an instinct *' determines its possessor to per- 
ceive" and in the third place "to pay attention." The 
impHcation seems to be that the perception and attention 
involved are conscious, and later on he asserts that instinc- 
tive actions are conscious. In any case it is doubtful if 
these terms can be used legitimately where there is no con- 
sciousness, so that he is again assuming the presence of psy- 
chic characteristics where they are not necessarily present. 

In the fourth place, he says that an instinct involves "an 
emotional excitement of a particular quality." It is cer- 
tainly true that many of the more complex instincts are 
accompanied by an emotion which is peculiar to the instinct 
it accompanies. But it is a grave error to assert this of all 
instincts. In fact, this assertion is quite contradictory to 
the prevailing theory as to the origin of emotions which was 
first formulated by Lange and James. According to this 
theory, emotions result from modes of behavior or bodily 
changes of some sort. It is therefore reasonable to suppose 
that if an instinctive action is always accompanied by a 
certain emotion, the emotion is caused by the action. The 
action must therefore have come into existence first in 
order to give rise to the emotion. It is possible that in 



The Nature of Instinct £21 

certain cases where an instinct has appeared suddenly as 
the resuh of a mutation of considerable extent, the emotion 
has appeared at the same time as the instinctive action. 
But in the great majority of cases the emotion must have 
come after the instinct. McDougall repudiates the James- 
Lange theory of emotions in certain respects, but he seems 
to accept it in its essential points, so that it is hard to under- 
stand why he insists upon an emotion for every instinct. 
In fact, it is hard to beheve that McDougall really thinks 
that every instinct possesses all the psychic characteristics 
he enumerates in this definition. It seems as if he must 
intend to apply this definition only to some of the most 
highly developed instincts. For these instincts this defi- 
nition may be accurate, and these psychic characteristics 
should be recognized, for, as McDougall says, ^'if we neglect 
the psychical aspect of instinctive processes, it is impos- 
sible to understand the part played by instincts in the 
development of the human mind and in the determination 
of the conduct of individuals and societies; and it is the 
fundamental and all-pervading character of their influence 
upon the social Ufe of mankind which alone gives tne con- 
sideration of instincts its great practical importance.'' ^ 
It may appear as if I am laying too much emphasis upon 
this point that an instinctive action does not necessarily 
involve any psychic, mental, or conscious processes. But 
from the point of view of this book such emphasis is essen- 
tial. It is one of my objects to show that the so-called 
psychic characteristics have been caused by the different 
forms of behavior, if indeed these characteristics are not 
in themselves forms of behavior, which possibility I shall 

* op. cit., p. 30. 



222 The Science of Human Behavior 

discuss later. As instinctive action is one of these forms 
of l.N^avior which have given rise to psychic phenomena, it 
is very important to emphasize its priority to these psychic 
phenomena. But by doing so I do not mean to imply that 
instinctive action is not very frequently intermingled v/ith 
and accompanied by psychic phenomena, and, as we shall 
see, there is an evolutionary continuity between instinctive 
behavior and intelligent and rational behavior which in- 
volves the highest psychic quahties. 

Definitions of Instinct 

We have now discussed briefly the most important as- 
pects of the general theory of instincts and are in a better 
position to define instinct accurately and in detail than we 
were at the beginning of this chapter. I shall, however, 
summarize the conclusions so far reached and discuss cer- 
tain other definitions before attempting to formulate one of 
my own. 

The first point discussed in this chapter was the relation 
of instinct to tropisms and reflexes. It was shown that 
some writers identify instincts with these other forms of 
behavior. But to do so is to destroy the utility of two of 
these terms. It is therefore preferable to limit their mean- 
ings somewhat so that they will have utiHty in distinguish- 
ing between different forms of behavior. I Hmited tropism 
to the reactions to external forces of animals without a 
nervous system. The term reflex I hmited to the reactions 
of animals with a nervous system. The term instinct I 
appHed to an integrated series of reflexes. 

We saw that instincts are based upon structural forms 
which are congenital. Consequently, instincts are in- 



The Nature of Instinct 223 

herited. An instinct may be manifested by but one in- 
dividual or by a very few, as when it is caused by a sudden 
mutation in structure. But usually an instinct character- 
izes a whole species. Instincts vary in accordance with 
changes in the structural forms upon which they are based. 
Instincts are not perfect, even according to a relative stand- 
ard of perfection, but they are usually adapted and conse- 
quently are usually ''practically serviceable." An instinct 
does not necessarily involve mental, psychic, or conscious 
quahties or phenomena. 

Any accurate definition of instinct must be in accordance 
with the above statements with regard to instinct. Let us 
see if any definition of instinct has been devised which is 
satisfactory both as to accuracy and as to the degree of 
detail with which it describes instinct. I have already 
mentioned and criticized a few. It would be impossible 
to quote all of the large number which have been suggested. 
I will mention but a few more which are more or less typical, 
some of which are among the most successful which have 
been devised. 

James' definition of instinct is as follows: *' Instinct 
is usually defined as the faculty of acting in such a way as 
to produce certain ends, without foresight of the ends, and 
without previous education in the performance." ^ It is 
evident, to begin with, that this is a very vague definition 
and might cover a tropism or a simple reflex action as well 
as an instinct. Furthermore, it makes instinct necessarily 
purposeful in its character which, as we have seen, is very 
objectionable. This is a typical example of a large number 
of definitions which are vague and emphasize too strongly 
1 op. cit., p. 383. 



224 The Science of Human Behavior 

the adaptive and purposeful character of instinct. It is 
rather strange that James should have formulated such a 
definition as this, for his conception of instinct seemed to 
have been based upon the nervous system and to have been 
quite clear-cut. This definition also does not state that 
instinct is hereditary, though this may be impHed in the 
statement that instinctive action does not require previous 
education. 

Lloyd Morgan has suggested the following definition : 
"From the biological point of view — instincts are con- 
genital, adaptive, and co-ordinated activities of relative 
complexity, and involving the behaviour of the organism as 
a whole." ^ Here again it is not stated expHcitly that 
instinct is based upon the nervous system, though the state- 
ments that instinctive activities are coordinated and that 
they are of relative complexity may be meant to imply it. 
It is also stated that instincts are adaptive. Aside from 
these points this is a fairly good definition and is less vague 
than most of them. As we have already seen, there may 
be difference of opinion as to whether an instinctive action 
must necessarily involve the organism as a whole. How- 
ever, it is probably better not to insist that an instinctive 
action must involve the whole organism, for there are many 
congenital activities which involve only a part of the or- 
ganism, but which are in every other respect exactly like 
the instinctive activities which involve the whole organism. 

Spencer's definition of instinct as "compound reflex 
action," which has already been quoted, is quite inadequate 
and has been misleading to many who thought that it iden- 
tified instinct completely with reflex action. But it em- 

^ op. cit., p. 27. 



The Nature of Instinct 225 

phasized the fact that instinct is based upon the nervous 
system and was therefore a long step in the right direction 
and influenced many later definitions. 

Perhaps the best definition of instinct which has so far 
/been formulated is the following: "An instinct is an in- 
^; herited reaction of the sensori-motor t3^e, relatively com- 
plex and markedly adaptive in character, and common to 
a group of individuals/' ^ While it is not stated expKcitly, 
the use of the phrase ''sensori-motor" implies that instinct 
is based upon the nervous system. It may, however, be 
questioned whether an instinctive action is always of the 
sensori-motor type. Earlier in this chapter has been dis- 
cussed the possibility of an instinctive reaction being stimu- 
lated by the image of an object which usually stimulates 
it or at first stimulated it. Such a reaction would be of the 
ideo-motor type. Furthermore it is stated that instinct 
is adaptive, which, as we have seen, is not necessarily the 
case. It is also stated that an instinct is common to a 
group, whereas we have seen that an instinct may belong 
to but one individual. So that it is evident that even 
though this may be the best definition which has so far 
been formulated, it has many faults. 

A New Definition of Instinct 

I have now cited enough examples to show that no one 
of the definitions of instinct which have so far been formu- 
lated is satisfactory. A good definition would, in the first 
place, accord with the facts and, in the second place, would 
be sufficiently detailed to distinguish instinct from the other 

1 In the article on Instinct, signed by J. M. Baldwin, G. F. Stout, and C. Lloyd 
Morgan, in the Dictionary of Philosophy and Psychology, edited by J. Mark Baldwin, 
New York, igoi. 
Q 



226 The Science of Human Behavior 

main types of behavior. What, therefore, should such a 
definition include ? In order to distinguish instinct from 
tropism, it must indicate that instinct is based upon the 
nervous system. In order to distinguish instinct from re- 
flex, it must indicate that an instinct is made up of an in- 
tegrated series of reflexes. In order to distinguish an in- 
stinctive activity from an internal physiological process, it 
must indicate that an instinctive activity is an external 
activity of the organism. I wish, therefore, to propose 
the following definition of instinct : — 
"^/^ An instinct is an inherited combination of reflexes which 
have been integrated by the central nervous system so as to 
cause an external activity of the organism which usually char- 
acterizes a whole species and is usually adaptive. 

It seems to me that this definition is accurate in every 
respect and that it is sufficiently detailed to distinguish 
instinctive behavior from the other main types of behavior. 



CHAPTER XII 

THE NEURAL BASIS OF INSTINCT 

The cerebrum and instinct, 228. — The cerebellum as the prin- 
cipal nervous mechanism for instincts, 228. — Localization of in- 
stincts in the spinal cord, medulla, and cerebellum, 230. — Impul- 
sive instincts, 230. — Chain instincts, 231. — Analysis of the nest- 
ing instinct of solitary wasps, 233. 

It is evident that according to my definition of instinct 
the mechanism of instinct must be studied in the nervous 
system. I believe that much of the writing on instinct 
has been of little or no value because this has not been done. 
No complete explanation of an instinctive action has been 
made until the nervous mechanism by means of which an 
external object has caused this action has been described. 
In order, therefore, to explain these instinctive actions, we 
must turn to the physiologists and neurologists. Unfor- 
tunately, however, as has been indicated in an earlier 
chapter, what is known with regard to the functions of the 
different parts of the central nervous system is still very 
meager as compared with the number of phenomena to be 
explained. It is impossible as yet to trace the nervous 
mechanism of most of the instinctive actions, especially 
the more complex ones, so that those who wish to explain 
instinctive actions fully must wait for physiology and neu- 
rology to furnish them more data. Consequently I shall 
discuss only very briefly the nervous mechanism of instinct 
and shall then pass on to a discussion of the external forces 

227 



228 The Science of Human Behavior 

at work in the evolution of instinctive actions and shall 
describe some of the principal instincts, especially those 
which are of special importance to man. 

Neural Mechanism of Instincts 

In a preceding chapter was given a brief summary of 
what is known as to the different kinds of reflex arcs and as 
to the functions of the different parts of the nervous system. 
We have seen that some reflexes are simple arcs on the 
spinal level. Other reflexes on the spinal level are con- 
nected with each other by loops so that they affect and 
influence each other. Still other arcs pass through the 
brain. Many of the reflexes on the spinal level could not 
be called instinctive because they do not cause an external 
activity of the organisms, or because they are too simple. 
This is true, also, of some of the reflexes which pass through 
the brain. But some of the reflexes on the spinal level are 
instinctive and probably still more of those which pass 
through the brain. 

The reflexes which reach the brain pass through different 
parts of it, and the question may be raised as to what parts 
of the brain are passed through by the reflexes which form 
instinctive actions. We have seen in a preceding chapter 
that the brain consists of four parts — the medulla oblongata, 
the pons, the cerebellum, and the cerebrum. The function 
of the medulla and the pons are in the main to connect the 
other parts of the brain with each other and with the spinal 
cord. The cerebellum seems to be the organ for coordina- 
tion in space and for the coordination of voluntary move- 
ments. Inasmuch, therefore, as many movements are 
determined through the cerebellum, it is probable that many 



The Neural Basis of Instinct 229 

instinctive actions are controlled by the cerebellum. The 
cerebrum, or at least the cerebral cortex, is the seat of the 
association centers, so that all of the higher mental faculties 
reside in the cerebrum. It is therefore not Hkely that many 
of the instinctive actions are controlled by the cerebrum. 
Indeed, it has been asserted by some that no instinctive 
actions are controlled by the cerebrum. For example the 
weU-known neurologist, Edinger, has made this assertion 
in the following passage: "All sense impressions and 
movement combinations belong to the palceencephalon} 
It is able to establish simple new relations between the two, 
but it is not able to form associations, to construct memory 
images out of several components. It is the bearer of all re- 
flexes and instincts. ^^ ^ He goes on to state that the function 
of the neencephalon or cerebrum is to form associations, thus 
furnishing the nervous basis for intelligent behavior. He 
thus draws a very sharp Une between instinctive and in- 
teUigent behavior by implying that the neencephalon has 
nothing to do with instinct and that the palaeencephalon 
has nothing to do with intelligence. However, if this is 
what he means, he is probably wrong, for it seems quite 
certain that the cerebrum has something to do with instinct, 
while it is quite possible that the rest of the brain has some- 
thing to do with intelligence, as we shall see in a later chap- 
ter. With regard to the connection between the cerebrum 
and instinct, "F. W. Mott and Pagano have given reasons 
for thinking that the emotions and instincts are organized 
in the optic thalami and corpora striata." ^ It has been 

1 Under this term Edinger includes all of the brain, aside from the cerebrum. 

2 Ludwig Edinger, The Relations of Comparative Anatomy to Comparative Psychol- 
ogy, in Jour, of Comp. Neurology and Psychology, Vol. XVIII, 5 (Nov. 1908), p. 444. 

' Carveth Read, Instinct, in the Brit. Jour, of Psychology, Vol. IV, Part i (May, 
XQIl), p. 9. 



230 The Science of Human Behavior 

found that the cry of distress, which is a very simple instinct, 
is located in the posterior corpora quadrigemina. Some if 
not all of the emotions, which are closely related to the 
instincts, are located in the cerebrum. For these reasons 
it is hard to believe that the cerebrum has nothing to do with 
instinct. To do so would be to make the break between 
instinct and intelUgence altogether too great. 

Impulsive and Chain Instincts 

However, it is undoubtedly true that the cerebrum does 
not have as much to do with instinct as the other parts of the 
central nervous system, but is more particularly the organ 
of intelligence. The instincts are localized in the main 
in the spinal cord, in the medulla, and in the cerebellum. 
Some of these instincts are very simple and are manifested 
in a single external action. This does not mean, however, 
that these actions do not involve a good many reflexes. 
These instincts are sometimes called impulsive instincts, 
and it seems plausible that they are localized in the spinal 
cord. This, however, is not true of all of them, as, for ex- 
ample, the cry of distress which has been mentioned. Other 
instincts are much more complex and involve a series of 
actions. It is probable that most, if not all, of these in- 
stincts are localized in the brain. These instincts may be 
complex because a single external stimulus arouses a reflex 
which is connected with a number of reflexes, each of which 
determines an external action, so that a series of such actions 
take place. Sometimes, however, these instincts are com- 
plex because the first action brings the organism under the 
influence of a new stimulus which causes the second action, 
and so forth. It may be questioned whether such a scries 



The Neural Basis of Instinct 231 

of actions could be called a single instinct in strict accord- 
ance with our definition of an instinct, since they seem to 
be a series of separate instincts. Such a series of instinctive 
actions is sometimes spoken of as a chain instinct, and 
inasmuch as such actions are inevitably bound to follow 
each other, and as they are coordinated v/ith each other, it 
may be legitimate to speak of such a series as an instinct. 

In the light of the preceding chapters on the nervous 
system it ought to be easy to understand the evolution of an 
impulsive instinct and of a complex instinct, which is made 
up of a series of actions which are determined by reflexes 
which are connected with each other in the central nervous 
system. In the case of these instinctive actions or series 
of actions, the actions follow close upon the stimulus, so that 
the connection of cause and effect is very evident. A study 
of the nervous system shows what the nervous mechanism of 
these types of instincts is, though we may not be able to 
trace the mechanism of each particular instinct. External 
forces are at work selecting out the reflexes which are useful 
and suppressing those which are harmful, so that these 
instincts are sure to be more or less adaptive. 

But it is more difficult to understand the so-called chain 
instincts because the causal connections are not so evident 
and because a long series of actions, sometimes more or less 
separated from each other in time and place, are so evidently 
leading up to some end that it is hard to believe that they 
are not directed by intelligence. This is true of many 
instincts, some of which are directed towards the preserva- 
tion of the individual and others to the reproduction of the 
species. An example of the first kind is where an animal 
stores up food during the summer to feed upon during the 



232 The Science of Human Behavior 

winter, while an example of the second is the making of a 
nest. It has frequently been thought that such behavior 
is in imitation of others. But this theory has been dis- 
proved many times by segregating a young animal from its 
kind before it has had the opportunity to observe such be- 
havior, and then finding that the instinct still manifests 
itself under favorable conditions. As has been indicated, 
it has also been thought that such behavior is intelligent. 
But a careful analysis of the facts in these cases and a study 
of the anatomical and physiological characteristics of these 
animals, combined with a knowledge of the nature of intel- 
ligence in general, shows in most of these cases that the be- 
havior could not possibly be intelligent. This will become 
more evident in a later chapter on intelligence. 

In the case of every chain instinct we start with a reflex 
which is stimulated by an external stimulus. This reflex 
may have, and in all probability has, been derived from a tro- 
pism. The action which results from this reflex may bring 
the organism under the influence of an external force which 
stimulates a new reaction. Or the first reflex action may 
cause a physiological change in the organism which stimu- 
lates a new reaction. Thus it is that a series of actions may 
become causally connected with each other. But such a 
series, thus determined by accident, as it were, would not 
necessarily have any utility. External selective forces, 
however, are always at work eliminating those which are 
harmful and sometimes, also, those which are merely use- 
less, and preserving those which are useful so that the 
actions and series of actions which persist are usually adap- 
tive. It seems almost incredible in the case of the more 
complex of these instincts that so high a degree of adapta- 



The Neural Basis of Instinct 233 

tion could have been attained without any consciousness 
of the end on the part of the animal. But when we con- 
sider that in most of these cases the instincts have existed 
through thousands of generations, we can see that the selec- 
tive forces have had enough time to accomplish their work 
of adaptation.^ 

Nesting Instinct of Solitary Wasps 

Read has given an excellent analysis of one of these 
chain instincts in his discussion of the nesting instinct of 
the solitary wasps. He has made use of data furnished 
in the main by Mr. and Mrs. Peckham, but also by Fabre, 
Lubbock, and other observers. As an example of such an 
analysis I will quote from his article^ at considerable 
length. 

"In attempting to explain the origin and development of these 
nesting instincts in solitary wasps, I shall assume the general prin- 
ciples of Natural Selection; namely, that variations of behaviour 
that are advantageous to the species may be inherited, and accumu- 
lated by inheritance, and fixed : so that in course of time very complex 
activities may, through the survival of those individuals that inherit 
them, and the failure in competition of individuals less well-en- 
dowed, become characteristic of the species as a whole. How useful 
these nesting habits are is shown by an interesting fact. The 
species of solitary wasp keep up their numbers century after 
century, age after age, although each female wasp has (compared 
with most insects, most fish, and even with many mammals) very few 
offspring — lays very few eggs — less than a score (as well as I can 

1 Cf. C. O. Whitman, Animal Behavior, in the Wood's Holl Biological Lectures, 
Boston, 1899. Whitman gives suggestive analyses of the evolution of various in- 
stincts as based upon structural organization. He analyzes, among others, the 
instincts of keeping quiet and rolling into a ball in worms and insects, of pouting 
and t\imbling in pigeons, of incubation in birds, etc. 

2 Carveth Read, Instinct, especially in Solitary Wasps, in the British Journal of 
Psychology, Vol. IV, Part i (May, 1911), pp. 1-32. 



234 The Science of Human Behavior 

judge) ; and this suffices, in spite of many parasites and other enemies. 
The fact illustrates the general rule of animated nature, that the 
greater the care taken of offspring, the fewer they are. . . . 

"But this nesting instinct is a chain instinct, a series of totally dif- 
ferent actions, and to explain it we must consider each step, and also 
the order in which the steps occur. In the first place, then, we observe 
that (i) to hide an egg in a hole or other shelter is plainly useful ; (2) 
so it is to hide or cover up the opening of the hole ; (3) to lay food by 
the side of the egg, or the egg by the side of the food, is useful, even if 
there is no nest; (4) to bring more food is useful, if it enables the 
larva to attain a better growth, or development or potentiality, be- 
fore the pupa stage ; (5) to kill living food, or paralyse it, is useful, 
that it may not injure the egg or young larva ; (6) to inspect the nest 
from time to time is useful, in spite of actual shortcomings; (7) to 
explore the neighbourhood and to identify the spot are useful actions, 
if the egg and larva are afterwards to be provided for ; (8) to return 
(or 'home') is useful. . . . 

"Such actions, being useful and immediately useful, will, if they 
occur in any individual, be perpetuated and tend to become specific ; 
but, in the second place, how do they occur ? Let us begin with the 
making of the nest. To dig a hole in the ground, or in the stump of 
a tree, or in the stalk of a shrub, or to build a mud cell, as some wasps 
and some bees do, without knowing what is to be done with it (for 
plainly they cannot know) — is not this an extraordinary operation ? 
To understand it we must show how it may arise from simpler ac- 
tions more commonly performed by animals, especially by insects, if 
possible by hymenoptera, and particularly wasps. We may assume 
that the pecuHar actions characteristic of wasps have been differ- 
entiated from a common ground. To find a shelter of some kind for 
itself or its progeny is an action common to most kinds of the higher 
animals and to very many insects. Amongst wasps it sometimes 
takes the form of creeping into a crack in a chff, or wall (since walls 
have come into existence), or into a hole in a tree, whether the crack 
or hole has been made by the ordinary wear and tear of nature, or 
by some other animal. . 

"It has often been objected to the theory of evolution that we 
never see any species in process of changing form or colour ; and the 
same objection might be urged against the evolution of instincts. 
It depends on an illusion similar to that impHed in the term 'fixed 



The Neural Basis of Instinct 2S5 

stars' : we cannot see the stars move, but we can calculate the direc- 
tion and velocity of the movement of very many of them from facts 
that can be seen. So no doubt species and their instincts are always 
changing, but much too slowly for us to notice it within the limits of 
our short lives. We can, however, sometimes find in natural history, 
without appealing to embryology, evidence of the changes that have 
probably been undergone, and may sometimes find a condition of 
things that seems to imply that a change is now in progress. In 
such a condition, perhaps, are these instincts I have just described. 
When a wasp catches its prey before digging a nest, the simplest 
supposition is that, at first, the prey was left meanwhile upon the 
ground. It was an improvement upon this when prey was first hung 
upon a plant until its grave was ready, but not so great an improve- 
ment as quickly to exterminate the other practice; and so we still 
see them existing side by side in the hfe of the same species. Natu- 
ralists who Uve 50,000 years hence may find that the more careless 
practice has been entirely lost, or only occurs by atavism in idiot- 
wasps. But, further, the whole double process of either capture and 
digging, or digging and capture, may be in a state of change: the 
latter seems to be the commoner; and since it gives greater safety 
and economises time and energy, it may be gradually exterminating 
the former course. 

"To understand the matter we must try to find how both processes 
arose. To begin with the case in which capture precedes digging. 
The capture and killing, or paralysing, of prey in order to lay an egg 
upon it, is itself a complex process, which must have had a history. 
We know two simple cases : first, the depositing of eggs upon animals 
already dead, as by the Blow-fly {Calliphora erythrocephala) , and by 
carrion-beetles {Necrophorus), and by parasitic wasps (Cerophales 
SLYid Pomp, subviolaceus) ; and, secondly, the depositing of eggs upon 
living prey. The latter course is adopted by many flies ; and amongst 
wasps by various species of IchneumonidcB, which lay their eggs upon 
living caterpillars on whose juices the larvae feed, and by some Bra- 
conidce, a closely alHed famfly; and Pompilus trivialis oviposits on 
living spiders. Since a living caterpillar upon which an egg has been 
laid is stiU exposed to the attacks of other parasites and enemies, it 
may give greater safety to kill it ; and this is shown to be probable 
by the comparatively great number of eggs deposited by Ichneu- 
monidce and Microgaster. But much greater safety is obtained if the 



236 The Science of Human Behavior 

prey is not only killed, but also hidden in a hole or cell. Necrophorus 
buries the carrion on which its eggs are laid ; and parasitic wasps lay 
eggs on victims already hidden, or about to be hidden, by other wasps. 
With one utihty depending upon another, the combination of killing 
or paralysing the prey with the hiding of it is not more improbable 
than the combination (say) of imitative colouration with imitative 
flight in some butterflies. . . . 

"To return to the nesting instinct: why do wasps seek any shel- 
ter for their eggs ; why construct cells, or creep into holes or crannies ? 
Do they foresee that their progeny have enemies ; do they understand 
danger and safety? We cannot suppose so much. Probably to 
explain this matter we must fall back upon primitive tropisms — 
phototropism, or thermotropism, or stereo tropism. These impulses 
in such highly evolved creatures as the wasps, may date from re- 
mote ancestors in an age before our wasps had become wasps, and 
may remain active in existing species under conditions in which they 
are still useful and so far as they are useful. Wasps love sunshine 
and warmth ; shun cold and wet ; as the shadows of the afternoon 
lengthen, nearly all of them seek some sort of shelter, some being 
content with leaves or grass, others requiring more substantial pro- 
tection. . . . 

"But granting an original tropism as the basis of nest-making, we 
are still required to explain why at a certain time the behaviour 
originally determined by this tropism becomes effective, contrary 
to the animal's usual habits, in the morning or middle of the day, so 
that it suddenly begins to burrow in the ground or to wall up a cranny. 
This is an example of a great class of problems presented by the exist- 
ence of critical points in the life-history of animals. Why do birds 
in autumn feel the impulse to migrate, in spring to build nests ; why 
does a caterpillar at a certain time begin to spin its cocoon, knowing 
nothing of the pupa stage upon which it is about to enter ? And so 
on. Such changes seem to depend (a) on external conditions of tem- 
perature, food-supply, etc. ; {b) on internal conditions, a certain ma- 
turing or modification of the organism, producing perhaps an uneasi- 
ness that is rcHeved by a certain action. In wasps the approach of 
the time for laying an egg brings on a complete change of behaviour, 
so that instead of sporting about amongst the flowers, paying no at- 
tention to insects or animals of any other species, she begins to burrow, 
or to catch bees or spiders. By merely natural-history methods we 



The Neural Basis of Instinct 237 

cannot explain this : it is intrinsically a physiological question. But 
perhaps Psychology will help us to something better than mere blank 
astonishment. . . . 

"If it seems difficult to develop such chain instincts as these wasps 
display by natural selection of occasional small variations, or even 
of considerable variations, such as the bringing of a second or third 
fly or bee, there has been plenty of time to do it in. Hymenoptera 
are found throughout the Tertiary strata, perhaps even in the middle 
of the Secondary (Jurassic) — a good many million years ago. Simi- 
lar species of wasps and ants with similar habits are found in North 
America and in Europe, and must be supposed to have spread when 
the Arctic regions were viable ; for so many resemblances can hardly 
be accounted for by such methods of migration as the occasional 
transportation of colonists by floating timber." 

These excerpts give some idea of the nature of Read's 
analysis. He does not describe the nervous mechanism 
and processes by which these actions are determined. This 
would be a very difl&cult thing to do in so small an animal 
as the wasp, and it will probably be a long time before this 
can be done. But we know enough about the nervous 
system to have reason to believe that these chain instincts 
are being determined by it in the wasps as in other animals. 
Read recognizes this when he says that the explanation of 
these instincts is *' intrinsically a physiological question." 



CHAPTER XIII 

THE PRINCIPAL HUMAN INSTINCTS AND GENERAL INNATE 
TENDENCIES 

The number of human instincts, 238. — The directing of in- 
stinctive tendencies by intelligence, 239. — Description of the prin- 
cipal human instincts, 240. — The classification of the instincts, 
244. — The nature of a general innate tendency, 245. — Imita- 
tion, 246. — Suggestion, 247. — Sympathy, 248. — Play, 248. — 
Emulation, 251. — Workmanship, 252. — Gregariousness, 252. — 
Habit, 254. 

Let us now turn our attention to the human instincts. 
Many lists have been prepared which are supposed to in- 
clude all or at least the most important of the human in- 
stincts. But there has been the greatest variation among 
these lists both as to what actions are to be included in 
the Hst as being instinctive and also as to the total number 
of human instincts. The last point is illustrated in the 
cases of Darwin and James. Darwin thought that man 
had fewer instincts than any other animal, while James 
thought that man had the largest number of instincts of 
any animal. It goes without saying that such a difference 
of opinion would arise primarily out of a difference of 
opinion as to what ought to be included. under the head of 
instinct. 

But there are other reasons back of this reason. Those 
who believe that man has very few instincts have usually 
been greatly impressed by the extent to which human 
actions are determined by intelligence. They therefore 

2S8 



The Principal Human Instincts 239 

assume that where intelligence has appeared, instinct has 
died out. Those who believe that man has numerous 
instincts may recognize fully the part now being played by 
intelligence. This, however, does not explain why man 
should have more instincts than other species, and I have 
seen no explicit attempt to explain this. I presume, how- 
ever, that the explanation in the minds of most of those 
who have taken this position, though no one of them may 
have stated it, is the following : As we have seen, instinc- 
tive actions are determined by the nervous system. Con- 
sequently, the number and the complexity of the instincts 
would depend upon the extent and the complexity of the 
nervous system. It is therefore to be expected that the 
higher animals v/ith their more extensive and complex 
nervous systems would have more instincts than the lower 
animals. This would be most true of man. 

But it is also true that these instincts are very frequently 
not at all obvious in the behavior of men, thus giving rise 
to the idea that man has few instincts. It has been shown 
how an instinctive tendency is inhibited by becoming 
concentrated upon one object which thereafter serves as 
the only stimulus for it. Where instincts are numerous 
they may be inhibited and therefore become apparently 
non-existent by neutralizing each other where they are 
contradictory. In all probabiHty, however, the principal 
reason why instincts apparently disappear in the higher 
animals and especially in man is because the instinctive 
tendencies are being guided and influenced more and more 
by past experience and therefore by intelligence. Thus 
while the instincts are still at work furnishing the primary 
motive power, they become more or less hidden from view 



£40 The Science of Human Behavior 

by these later mental phenomena. James has described 
this situation very well in the following words : ''Wherever 
the mind is elevated enough to discriminate; wherever 
several distinct sensory elements must combine to dis- 
charge the reflex arc ; wherever, instead of plumping into 
action instantly at the first rough intimation of what sort 
of a thing is there, the agent waits to see which one of its 
kind it is and what the circumstances are of its appearance ; 
wherever different individuals and different circumstances 
can impel him in different ways, — wherever these are the 
conditions, we have a masking of the elementary con- 
stitution of the instinctive Hfe." We have already seen 
that even in the lower species instinctive actions are not 
absolutely invariable and predictable. For the reasons 
stated above, these actions in the higher species become far 
more variable and far less predictable. 

The Principal Human Instincts 

Let us now consider some of the lists of human instincts 
which have been prepared. The first will be James' list 
of what he considers the principal human instincts. As 
^ might be expected of James, the list is quite extended. 
First he mentions a number of simple reactions which the 
psychologists call impulses and which many writers have 
regarded as being mere reflexes without being instinctive. 
Among them are the following acts which characterize 
infants very early in life : Crying, sneezing, snuffing, 
snoring, coughing, sighing, sobbing, gagging, vomiting, 
hiccuping, starting, moving the limbs when tickled, touched, 
or blown upon, etc. If any one of these reactions is a 
simple reflex, it does not fall under my definition of an 



The Principal Human Instincts Ml 

instinct. But if it is an "inherited combination of re- 
flexes, " it is evident that it must fall under my definition, 
for every one of these actions is external. Then he men- 
tions a number of more complicated actions which appear 
very early in the Hfe of the infant and which are still more 
certainly instinctive in their character. Among these are 
the following: Sucking, biting, clasping, carrying to the 
mouth of an object, smiling, turning the head aside as a 
gesture of rejection, holding head erect, sitting up, stand- 
ing, locomotion, vocalization, etc. 

, / We now come to very complex forms of behavior, and it 
may be questioned whether some of them are distinct in- 
stincts. Among them James names the following : Imi- 
tation, emulation or rivalry, pugnacity, anger, resentment, 
sympathy, the hunting instinct, fear, appropriation or 
acquisitiveness, constructiveness, play, curiosity, sociabil- 
ity, shyness, secretiveness, cleanliness, modesty and shame, 
sexual love, jealousy, parental love. 

^ It is very doubtful if imitation can be considered an 
instinct, since it does not involve any specific reflexes or 
mode of behavior. In the course of imitation any kind of 
act may be performed. As we shall see, imitation is caused 
by suggestion and is like instinct only in that the tendency 
to imitate is inborn. Much the same can be said of emu- 
lation or rivalry. It certainly does not involve any specific 
reflexes or mode of behavior. In the course of rivalry any 
kind of act may be performed. It is probable that it is 
to a certain extent imitation, but imitation which is stimu- 
lated in part at least by the instinct of pugnacity. I shall 
discuss it later as one of the general innate tendencies. 
Pugnacity is in all probabiHty an instinct, since it usually 



242 The Science of Human Behavior 

involves a well-defined mode of action. But anger and 
resentment are simply emotions which accompany pugna- 
cious acts, and as such cannot be called instincts. 

Sympathy is primarily a state of feeling. Various acts 
result from this state, but they are very diverse in character, 
and so far as sympathy impHes external action, it is a general 
innate tendency. 

The inborn tendency to hunt is in all probability an 
instinct, since it involves a well-defined mode of action. 

Fear is an emotion rather than an instinct, but it usually 
accompanies an instinctive act, the most frequent one being 
flight. 

Appropriation or acquisitiveness is probably an instinct. 
Constructiveness may possibly be an instinct, though it 
involves a good many different kinds of action. 

The tendency to play is undoubtedly inborn, but it in- 
volves so many different kinds of action that it can hardly 
be regarded as a distinct instinct. It is rather a general 
innate tendency. 

Curiosity may have an instinctive basis, but in man is in 
large part an intelligent phenomenon. 

Sociability and shyness are undoubtedly inborn, but are 
so general that it is doubtful if they are distinct instincts. 

Secretiveness and cleanliness are probably instincts, since 
they involve fairly definite modes of action. 

Modesty and shame certainly are not instinctive, as 
James himself admits in his discussion of them. 

Sexual love is, strictly speaking, an emotion. But the 
sexual instinct is one of the most powerful of the instincts. 
Jealousy is an emotion which is aroused when sexual love 
is violated or the sexual instinct is thwarted, and may ac- 



The Principal Human Instincts 243 

company various instinctive acts usually pugnacious in 
their character. 

Parental love is, strictly speaking, an emotion. But the 
parental instincts which cause parents to care for their 
young are very important instincts. 

The difficulty involved in determining in the case of many 
of these modes of behavior whether or not they are instinc- 
tive is that we do not know what nervous mechanism is in- 
volved. All of the modes of behavior which have been 
discussed are probably inborn, with the exception of mod- 
esty and shame, but we cannot be sure in every case 
whether there is involved a sufficiently definite combination 
of reflexes to justify calling it an instinct. Where, how- 
ever, we find a great variety of acts grouped under the head 
of one instinct, as in so many of the above cases, it is hard 
to believe that it is an instinct, but rather a general innate 
tendency which involves a good many different kinds of in- 
stinctive acts. These tendencies will be discussed more 
fully later in this chapter. 

.Angell ^ says that the generally recognized instincts in 
man are the following: *'Fear, anger, shyness, curiosity, 
affection, sexual love, jealousy and envy, rivalry, socia- 
bility, sympathy, modesty (?), play, imitation, construc- 
tiveness, secret! veness, and acquisitiveness." Angell says 
elsewhere 2 in this book that instincts "represent structur- 
ally preformed pathways in the nervous system, and stand 
fimctionally for effective inherited coordinations made in 
response to environmental demands.'' In view of this 
;j^ -^.tement il ?s strange that he should include as instincts 
such general tendencies as imitation and play, which do 

1 James R. Angell, Psychology, p. 349. 2 Qp^ ciL, p. 339, 



244 The Science of Human Behavior 

not represent any specific pathways or coordinations in the 
nervous system, but which manifest themselves through 
many reflexes and combinations of reflexes. I have already 
commented upon all in his list with the exception of affec- 
tion and envy. Both of these are emotions which are fre- 
quently accompanied by instinctive actions. 
^ McDougall ^ gives the following Hst of what he considers 
the principal human instincts : FHght, repulsion, curiosity, 
pugnacity, self-abasement, self-assertion, parental, repro- 
ductive, gregarious, acquisitive, constructive. I have 
already commented upon most of these and will speak 
briefly of the others. Flight is undoubtedly an instinct 
and is usually the instinctive act which is in mind when 
fear is spoken of as an instinct. Repulsion is probably a 
distinct instinct. Self-abasement and self-assertion are 
probably innate tendencies, but it is hard to say whether 
they are sufficiently specific to be called instincts. Mc- 
Dougall associates very closely with each of these instincts 
an emotion which is aroused by it. The subject of emotion 
I shall discuss in a later chapter. He also discusses some 
of the general innate tendencies which will be taken up 
further on in this chapter. 

Several writers have tried to classify the instincts ac- 
cording to the ends which they accomplish, as, for example, 
when they are classified according to whether they pre- 
serve the individual, the species, or society. It is true 
that some distinction may be made between instincts 
according to the above criterion. And yet the instincts 
are so closely bound up together that it is dangerous to 
make very much of such distinctions. After all, the in- 

^ Socuil Psychology, chap. HI. 



The Principal Human Instincts 245 

stincts, Kke all other characteristics of organic matter, are, 
so far as they have any end, directed towards the general 
end of increasing the amount of living matter. So that 
the preservation of the individual, the species, and of 
society in the long run aid each other and accompHsh the 
general end of increasing the amount of living matter. 
And frequently it is impossible to determine whether an 
instinct preserves one of these three any more than it does 
the other two. 

Furthermore, the attempt to classify instincts according 
to such a criterion usually leads to the inclusion under the 
head of instinct of every mode of behavior which attains 
these ends, even though many of them are far too complex 
to be regarded as instincts. We have a good example of 
this in the case of the psychologist, Henry Rutgers Marshall, 
who in his work entitled Instinct and Reason classifies the 
instincts as follows : (i) instincts of individuahstic import, 

(2) instincts relating to the persistence of organic species, 

(3) instincts relating to the persistence of social groups. 
Then imder these heads he recognizes ethical, patriotic, 
benevolent, and artistic instincts, while most of his book 
is devoted to tr3dng to prove that there is a rehgious in- 
stinct in man which has had biological and social value. 
As we have already seen, all of these ^'instincts" are very 
complex modes of behavior which are made up of instinc- 
tive, habitual, and intelHgent actions which have become 
closely associated with each other. 

General Innate Tendencies 

Let us now turn to the general innate tendencies and 
discuss them briefly. As we have already seen, there are 



246 The Science of Human Behavior 

certain general, inborn modes of behavior which are re- 
garded by many as distinct instincts, but which cannot 
rightfully be regarded as such, because at different times 
they involve totally different parts of the nervous system. 
Inasmuch as an instinct has a specific neural mechanism 
which is utiHzed every time the instinctive action takes 
place, a mode of behavior which involves at different times 
entirely different parts of the nervous system cannot be 
regarded as an instinct. 

As we have seen, imitation cannot be regarded as an 
instinct, because it involves very different modes of be- 
havior. Furthermore, there are certain kinds of imitation 
which are not caused by an inborn tendency. Rational 
imitation which results from experience and intelHgence 
will be excluded from the present discussion. Taking, then, 
the imitation which results from an inborn tendency, let 
us see what is its nature. It is evident that imitation 
cannot take place until the act in question has first been 
performed by another. It is then performed by the imi- 
tator, because he has seen the act performed or has in some 
other way become aware of its performance. The act 
may be an instinctive one and therefore one which is 
usually aroused by certain appropriate stimuU which are 
directly connected with the neural mechanism of the in- 
stinct. But when the act is imitated, it is not aroused by 
external stimuli which are directly connected with the 
neural mechanism of the instinct. The centers in the nerv- 
ous system which are stimulated by these external stimuli 
must therefore be connected within the central system 
with the motor centers for the instinctive act. It is there- 
fore evident that imitation is ideo-motor action. It is an 



The Principal Human Instincts 247 

innate tendency in the sense that the association centers 
in the brain make it possible for the motor centers of this 
mode of action to be aroused from other centers which 
have been stimulated by external stimuli coming from the 
performance of this act by another. These stimuli may 
be visual, auditory, olfactory, tactile, etc., in their char- 
acter, but whatever they may be they are connected with 
the motor centers for certain modes of action and may 
prove effective thus indirectly to stimulate these modes of 
action. 

This process by which a stimulus is transmitted from a 
receptor center by means of an association center to a 
motor center is suggestion, and the suggestibihty of an 
individual depends upon the ease with which such trans- 
linission takes place within his central nervous system. I 
am well aware that suggestion is frequently defined other- 
wise, as when the communication of an idea from one indi- 
vidual to another is called suggestion. But I believe that 
my definition is the only correct technical one for this 
process. It is usually assumed that suggestion leads to 
action of the sort suggested more or less directly and, if 
this be the case, it must be by means of such a process as 
has been defined above as suggestion. It is true that com- 
munication of an idea may lead to action, but the connec- 
tion in that case is much more indirect and the process 
much more comphcated. Suggestion is sometimes called 
a general innate tendency. But if it is meant to imply by 
this that it is an external form of behavior, it certainly is a 
mistaken definition. For, as we have seen, suggestion is a 
purely internal process, but leads to an external mode of 
behavior in the form of imitation. 



248 The Science of Human Behavior 

Sympathy also, like suggestion, is an internal process 
which leads to the stimulation in one person of an emotion 
already experienced by another. Like suggestion it also 
has been mistakenly called a general innate tendency in 
the sense of being an external mode of action. But so- 
called sympathetic action is nothing more than imitative' 
action which is accompanied by sympathetically induced 
emotion. 

Playful activities are very widespread among living 
beings. Play may be defined as the expenditure of energy 
purely for the sake of gaining pleasure without being 
directed towards any useful purpose. At any rate, no use- 
ful purpose can be the immediate object of play, though, 
as we shall see, it may serve some useful purpose in the 
long run. Playful activities are most frequent among thne 
young, who very often spend all their time in play. The 
simplest theory of play is the Schiller-Spencer surplus 
energy theory of play. According to this theory, animals 
play in order to get rid of what energy they have left over 
after they have completed the activities necessary for 
existence. There is undoubtedly a great deal of truth in 
this theory. It is a well-known physiological fact that an 
organism cannot remain healthy unless it performs its 
functions to a normal degree. In order to perform these 
functions it has to expend a certain amount of energy. 
It is stimulated in the first place to perform these func- 
tions by the necessities of existence. If these necessities 
require it to expend the normal amount of energy, it will 
become normally tired and will not need to expend any 
more energy. 

The surplus energy theory of play therefore explains in a 



The Principal Human Instincts 249 

general way why animals expend energy in ways which are, 
to say the least, not immediately useful. But this theory 
does not explain the forms these activities take. If play is 
nothing more than the expenditure of surplus energy, it 
might be expected that it would be nothing more than form- 
less activity. But, as a matter of fact, playful activities 
take on very definite forms, and these forms are suggestive 
of their nature and origin. The noticeable thing about 
them is that they resemble certain instinctive activities. 
Thus the plays of the boy seem to reveal the presence in 
him of the hunting and combative or pugnacious instincts, 
while the little girl playing with her dolls reveals an early 
awakening of the maternal instinct. It is true that imita- 
tion has a good deal to do with determining the playful 
Activities of the young. Very frequently these activities are 
nothing more than imitations of the activities of their 
elders. But when such playful activities are quite spontane- 
ous, that is to say, do not copy in any way the activities of 
the adults among whom these young live, it is usually 
possible to detect strong Hkenesses to instinctive activi- 
ties. A good way to test this is to separate entirely from 
the earhest age the young of a species from adults of the 
same species and then observe the playful activities which 
spontaneously manifest themselves among these young. 
For example, if a number of very young puppies are 
isolated from other dogs, it is certain that as soon as 
their eyes are open and their legs are strong enough for 
them to move around easily, they will begin to fight each 
other in play, thus reveahng an early awakening of the com- 
bative instinct. But the instinctive impulse will not dis- 
play itself in its full strength, for they will not usually 



250 The Science of Human Behavior 

hurt each other, but will simply go through the motions of 
fighting. Apparently, therefore, the inborn, integrated 
series of reflexes upon which the combative instinct is 
based is already beginning to function, though not yet 
with the faciHty and force it will display as maturity is 
reached. Thus it appears, as has been well shown by 
Groos,^ that playful activities take the form, to a large 
extent, of early manifestations of instinctive impulses which 
will attain full force as maturity is reached. And as has 
been pointed out by Groos and others, such playful activi- 
ties have great utiHty for the young after they have grown 
up and for the species, for in these playful activities skill is 
acquired in the practice of the instinctive activities which 
will have great utility later in life. Thus we see why it is 
that though playful activities have no immediate utiHty ne 
they may have great utiHty for the future. 

It is also true of the playful activities of adults that they 
are to a large extent the manifestation and expression of 
instinctive impulses. Thus in most games are involved 
opposition and conflict, which are undoubtedly manifesta- 
tions of the combative instinct. Indeed, it has become truc.- 
in our modern civiHzed society that some instinctive impulses 
now find their expression for most individuals only in the 
form of play. For example, few people to-day need to hunt 
for purposes of securing subsistence, which was undoubtedly 
the original cause for the growth of the hunting instinct, 
but many indulge in hunting for purposes of play. While 
the UtiHty of playful activities, the forms of which are de- 
termined by instinctive impulses, has been shown for the 

1 Karl Groos, The Play of Animals, translated from the German, New York, 
1898. The Play of Man, translated from the German, New York, igoi. 



The Principal Human Instincts 251 

yoiing, it is perhaps unfortunate that the same should be 
true to so great an extent for adults, for if playful activities 
differed greatly from purely instinctive activities, there 
would be greater variety in human behavior, and human 
personahty would be correspondingly more complex. 

It must now be evident that very different kinds of activi- 
ties are included under the head of play. If, therefore, an 
instinct is what I have defined it, namely, an integrated 
series of reflexes, play certainly is not a specific instinct, 
as some writers have contended. The inborn physiological 
characteristics require that surplus energy be expended, and 
the instincts furnish well-worn grooves into which the ex- 
penditure of this energy may fall, so that playful activities 
frequently are also instinctive activities, but taken together 
ley do not constitute a distinct instinct. 

Emulation or rivalry, which, as we have seen, is regarded 
by some writers as a specific instinct, is much the same kind 
of a mental phenomenon as imitation or play. As has been 
stated, it does not involve any one integrated series of 
reflexes, and in the course of emulation an individual may use 
h\ny different kinds of behavior. As a matter of fact, 
emulation is to a large extent imitation stimulated in part 
at least by the combative or pugnacious instinct. Other 
instincts are involved according to the object of emulation 
or rivalry. For example, if it is rivalry in love, the sexual 
instinct plays a part. If it is rivalry in economic activities, 
the instinct of acquisition plays a part. Thus under the 
head of emulation we place certain complex groups of ac- 
tivities which as groups bear certain Hkenesses to each 
other. These groups include many activities which are 
instinctive. 



252 The Science of Human Behavior 

Another so-called instinct is the *' instinct of workman- 
ship." ^ It is evident that the tendency to work involves 
many different kinds of activity. Work may be defined as 
being effort devoted to the production of things of value. 
Like play, it is undoubtedly due in part to the physiological 
need of the organism to expend a certain amount of energy. 
But it is also and in large part due to the needs of sub- 
sistence which force the individual to expend effort in ordei* 
to secure the things needed. In human society this takes 
the form of economic pressure in the economic struggle for 
existence. This effort is directed and its character is deter- 
mined in part by numerous internal factors. Among them 
are instincts such as the instinct of constructiveness, which 
has been discussed, and various feelings and emotion? 
which will be discussed in later chapters. Furthermdr<i^^ 
intellectual factors play a more and more important part, 
especially among men. Various compounds of instincts, 
intellectual characteristics, and feelings arise which play a 
part in directing the tendency to work. Among them may 
be mentioned aesthetic characteristics, such as the so-called 
architectonic sense, ambition to secure wealth, power, Cc^^'*'^ 
certain altruistic sentiments, etc. This effort is also di- 
rected and its character determined in part by numerous 
factors of the physical and social environment of the in- 
dividual. So that it must be evident that this so-called 
''instinct of workmanship" is very complex in its character 
and causes, and very far from being a distinct instinct. 

Many writers recognize a distinct instinct of sociability 
or gregariousness. It is true that many of the higher species 

' Thorstein Veblen, The Instinct of Workmanship and the Irksomeness of Labor, 
in the Am. Jour, of Sociology, Vol. IV, No. 2 (Sept. i8q8), pp. 187-201 ; The Theory 
of the Leisure Class, New York, 1899. 



The Principal Human Instincts 253 

are gregarious, so that the members of these species live in 
more or less constant association with each other. Further- 
more, frequently there does not seem to be any other reason 
for such association than an innate impulse causing these 
sociable animals to come together. This is probably why 
so many have thought that there must be a gregarious 
instinct. But when we apply our definition of an instinct 
as an integrated series of reflexes, it is hard to beHeve that 
there is any such specific series of reflexes which causes 
association. However, it is certain that the primary causes 
of association were instincts so far as association came about 
through subjective causes, while ever since they have been 
powerful forces for association. The principal ones of these 
instincts undoubtedly are the sexual and the parental 
instincts. But habit also has a great deal to do with gre- 
gariousness. The young of all the higher species are help- 
less for a certain period of time and have to be cared for by 
their parents. During this time the habit of association 
becomes deeply rooted. Furthermore, during this period 
imitation leads them to act Hke their fellows. Thus it is 
that these habits mightily reenforce the instincts which 
lead to gregariousness. We should also not ignore the 
external forces which drive members of the same species 
together. Frequently the food and drink of a species are 
to be found only at certain places, so that the members of 
the species are forced to gather at those places, as, for exam- 
ple, at the salt licks where the American bison used to gather. 
Or the members of a species are forced to come to certain 
places for shelter or protection. Natural selection is at 
work determining the extent to which a species is to become 
gregarious. As a general thing it is the weaker species, 



254 The Science of Human Behavior 

which are therefore preyed upon, which become the most 
gregarious, for the less sociable members who wander from 
the protection of the flock or herd are pretty certain to be 
destroyed. The strongest species, Kke the lion, the tiger, 
the hawk, etc., which have Httle to fear from other species 
and which spend their time in preying upon the weaker 
species, are usually very unsocial. 

In human social evolution many conscious and rational 
forces are at work bringing about association in the form of 
mutual aid and cooperation and, above all, in the division of 
labor. But I cannot stop to discuss these causes of as- 
sociation in this chapter. Enough has been said, I think, 
to show that the forces which bring about association are 
very complex and that it is very doubtful if there is any 
specific instinct of gregariousness. In later chapters on, 
social evolution the causes of association will be analyzed 
more fully. 

So far as I know, no one has called the tendency to form 
habits an instinct, but it has been called a general innate 
tendency, and its relation to instinct should be briefly noted. 
It is undoubtedly the tendency of all living organisms to 
perform an action more easily on repetition. After this 
ease has been gained, the act is spoken of as a habit. But 
the question may be raised as to what kind of an act it was 
before the habit was formed. It is evident that it must 
have been some form of inborn reflex action and may have 
been instinctive. A habit may therefore grow directly 
out of an instinct, so that the connection betweeen instinct 
and habit is very close. A habit may be an instinctive 
mode of action which has become reenforced through rep- 
etition, or it may be a combination of instinctive modes of 



The Principal Human Instincts 255 

action. The tendency to form habits is inborn, while the 
modes of action which are to become habitual are at first 
inborn, though they may vary in the course of habitual use. 
Lloyd Morgan has called these habits which grow out of 
instincts "instinct-habits," which phrase emphasizes the 
close connection between instinct and habit. 

Habits are sometimes spoken of as reflex actions. Ac- 
cording to the strict definition of reflex action which I have 
been using, this is not accurate, for reflexes are inborn, while 
habits are acquired. The reason for speaking of habits as 
if they were reflexes is that habitual acts are frequently 
performed in the same more or less invariable and uncon- 
scious fashion as reflex acts. It is true that habits are 
formed by reenforcing or combining reflex and instinctive 
actions, so that habits are always based upon reflexes, but as 
habits are not mere reflexes. 

The discussion of instinct in these chapters must, I think, 
have shown that our knowledge of instinct will depend in 
the main upon our knowledge of the nervous system. It 
is impossible to define instinct in general, to determine 
what are the specific instincts, or to describe the mechanism 
of these instinctive actions apart from the nervous system. 
There is, probably, no more important fine of investigation 
for the understanding of the behavior of the higher animals 
than the study of the nervous system. 



CHAPTER XIV 

THE NATURE OF INTELLIGENCE 

Psycho-physical processes, 256. — Introspection, 257. — Intel- 
ligent behavior as the result of experience, 258. — Associative 
memory as a criterion of intelligence, 260. — Unspecialized nervous 
tissue essential for intelligence, 262. — The cerebral cortex as the 
neural basis for intelligence, 263. — The central nervous system as 
the organ of memory, 265. — The range of intelHgence in the ani- 
mal world, 267. — The structural advantages of the vertebrate for 
the development of intelHgence, 269. — The reasons for man's 
superior intelligence, 270. — The nature of learning, 273. — Sen- 
sations, 274. — Images, 274. — Memory, 275. — Sensori-motor and 
ideo-mo tor action, 275. — Pleasure and pain as reenforcing and 
inhibiting ideo-motor action, 275. — Ideas, 277. — Thought as a 
flow of ideas, 277. — Concepts as generalized images, 278. — Image- 
less thought, 278. — Reason, 279. — The nature of human intelli- 
gence, 280. 

I HAVE now discussed the three important forms of be- 
havior, the tropism, the reflex action, and the instinctive 
action. Each of these is external ; that is to say, it is a 
movement of an animal or part of an animal which is visible 
from the outside. It may be that we are not justified in 
calling any movement of the organism which is not visible 
from the outside a form of behavior. But there are cer- 
tain internal movements which are physiological processes 
like these forms of behavior, and which have great influence 
over certain kinds of behavior. These internal processes, 
consisting of numerous minute and refined movements, 
most of which are within the nervous system, are usually 

256 



The Nature of Intelligence 257 

called psycho-physical processes, and collectively they deter- 
mine what are called mental phenomena. Because of the 
important part played by these processes in the deter- 
mination of the behavior of the higher animals, we must 
now consider them. They will be discussed under the heads 
of intelligence and consciousness, while at the end of this 
discussion I shall state my conception of their fundamental 
nature in the form of a theory of mind. 

The study of mental phenomena has always presented 
great difficulties. Because the movements involved are 
internal and are very minute and refined in their character, 
they are more or less intangible and difficult to observe. 
So far the method used in studying mental phenomena has 
been subjective and introspective rather than objective. 
Introspection must always be an important source of in- 
formation with regard to mental phenomena, but I do not 
believe that the study of mental phenomena can become 
thoroughly scientific until the method used is in the main 
objective. The present study will therefore be from the 
standpoint of behavior and will consequently be objective, 
though occasional recourse to introspection will be made. 

Nature or Intelligent Behavior 

The phrase *' intelligent behavior" is frequently used, the 
use of which may seem to imply that intelligence is a form of 
behavior, or, at any rate, that it is an organ which deter- 
mines that form of behavior. As a matter of fact, however, 
it is not a distinct organ, but stands in the same relation to 
intelligent behavior that instinct stands to instinctive ac- 
tion. Let us see what are the pecuHar features of intelHgent 
behavior. Such behavior always grows out of experience. 



258 The Science of Human Behavior 

No organism without individual experience can display 
intelligent behavior. Intelligence is not inherited, but is 
acquired by the individual. Intelligent behavior is not an 
inherited form of reaction, though it is based upon and makes 
use of inherited modes of behavior. It is, in fact, a modifi- 
cation of an inherited mode of behavior due to experience 
and is consequently more varied usually than inherited 
modes of behavior, though, as we have seen, inherited 
modes of behavior also may vary somewhat. 

Intelligent behavior is therefore made up of tropic, reflex^ 
and instinctive actions which have been combined in new ways 
as a result of experience so as to constitute new forms of behavior. 
It is evident, therefore, that the organism must be amenable 
to the effects of its experience in order to develop these 
new forms of behavior. In other words, the organism must 
possess a certain degree of plasticity, and in this plasticity 
we find the necessary structural basis for intelHgent be- 
havior. Now it goes without saying that all organisms 
possess a certain degree of plasticity. This is due in the 
first place to the fact that all matter is affected by the forces 
which play upon it. But in the second place the protoplasm 
of which all organisms are constituted is peculiarly sensitive 
to external forces. So that all organisms are more or less 
plastic, and the behavior of every organism is being affected 
by its experience, as has been shown in the preceding study 
of inherited forms of behavior. But the degree of variation 
in behavior which is sufficiently great to justify calling it 
intelligent requires an unusually high degree of plasticity. 
It requires parts of the organism which are unusually sensi- 
tive to the effects of experience and which are specially de- 
voted to combining and rearranging the inherited modes of 



The Nature of Intelligence 259 

behavior. The principal example of this is the unspecial- 
ized correlation tissue or gray matter of the nervous system. 
In fact, we may find that no intelHgent behavior is possible 
without the presence in the organism of this gray matter. 
In the hght of the preceding remarks it is evident that 
it is important to determine where the Hne is to be drawn 
between the plasticity in behavior which is common to 
all organisms and the plasticity which may be called in- 
telHgent. It is true that some writers have refused to 
draw any such Hne and have insisted that all organisms are 
capable of intelHgent behavior. For example, some of the 
students of the behavior of the lower organisms, who have 
naturally been impressed with the continuity in the develop- 
ment of behavior, attribute intelHgence even to the lowest 
organisms when their behavior varies in accordance with 
experience. This is true of Jennings, who, as we have seen, 
always tends to minimize the differences between the be- 
havior of the lower and that of the higher organisms. He 
endeavors to show that perception, discrimination, choice, 
attention, pain, fear, memory, habit, and consciousness are 
to be found in a rudimentary form even in the protozoa.^ 
As we have seen, the work done by Jennings and his fellow- 
workers has been of the greatest value in tracing the evolu- 
tion of behavior and in emphasizing its continuity. But 
if intelHgence is extended to all organisms, the term will lose 
its value for distinguishing between different kinds of be- 
havior, just as we have seen the term instinct would lose 
its utiHty if it was reduced to reflex action, and the term 
reflex would lose its utiHty if it was reduced to tropism. 
It is therefore better, I believe, to restrict the term intelH- 

1 Behavior of the Lower Organisms, New York, 1906, pp. 329-337. 



260 The Science of Human Behavior 

gent to certain of the more complex variations in behavior 
and to formulate a criterion for distinguishing between 
intelligent and unintelligent behavior. 

Associative Memory 

What, then, is to be this criterion ? Various attempts 
have been made to formulate such a criterion. Perhaps the 
best-known one is the theory that associative memory or the 
power of forming associations is the mark of intelligence. 
One of the principal exponents of this theory is Loeb, who 
defines associative memory as follows: ''By associative 
memory I mean that mechanism by which a stimulus brings 
about not only the effects which its nature and the specific 
structure of the irritable organ call for, but by which it 
brings about also the effects of other stimuh which formerly 
acted upon the organism almost or quite simultaneously 
with the stimulus in question. If an animal can be trained, 
if it can learn, it possesses associative memory." ^ Again 
he characterizes it as follows: ''By associative memory I 
mean the two following peculiarities of the central nervous 
system : First, that processes which occur there leave an 
impression or trace by which they can be reproduced even 
under different circumstances than those under which they 
originated. . . . The second peculiarity is, that two processes 
which occur simultaneously or in quick succession will 
leave traces which fuse together, so that if later one of the 
processes is repeated, the other will necessarily be repeated 
also." ^ Loeb speaks of associative memory primarily as 
the criterion of consciousness and of psychical phenomena 

* Comparative Physiology of the Brain and Comparative Psychology, New York, 
1900, p. 12. « Op. cit., p. 213. 



The Nature of Intelligence 261 

in general, but it is evident that he is including intelligence 
under this head. 

Various other writers have adopted this theory of the 
criterion of intelligence, among them being Holmes,^ Lloyd 
Morgan, Forel, Bethe, etc. But there have also been severe 
critics of this theory, among them being Yerkes,^ ClaparMe,^ 
and Jennings.* The essence of their criticism is that 
associative memory simply means the ability to learn, and 
that this ability is possessed by all organisms. It is evident 
that by the ability to learn they mean merely the capacity 
to be modified, which, as we have seen, is possessed by all 
protoplasmic matter. If the ability to learn simply means 
this modifiabiHty, and if associative memory is nothing more 
than this abiHty, it is evident that this criterion is of no 
value, for in that case associative memory and all that 
its presence implies would characterize the whole organic 
world. Let us see whether such is the case. 

It is true that Loeb says that if an animal can learn, it 
possesses associative memory. But it may be that he has a 
special kind of abiHty to learn in mind, and an analysis of 
his definition shows that he has. The kind of learning he 
has in mind is indicated when he says that associative mem- 
ory is present when a stimulus arouses not only the response 
which is pecuHar to it, but also a response which is pecuHar 
to a stimulus which has previously acted upon the or- 
ganism. It is evident that this cannot happen unless the 
animal has a mechanism which keeps a record of the move- 

* S. J. Holmes, The Beginnings of Intelligence, in Science, March 31, 1911. 

2 Animal Psychology and Criteria of the Psychic, in the Jour, of Phil. Psych, 
and Sci. Meth., Vol. II, No. 6 (March 16, 1905). 

' E. Claparede, The Consciousness of Animals, in the International Quarterly, 
Vol. VIII (Dec-March 1 903-1 904). * Op. cit., p. 334. 




262 The Science of Human Behavior 

ment stimulated by the previous stimulus so that when it is 
stimulated by the second stimulus it can reproduce the pre- 
vious movement. It is possible that an organism without a 
nervous system could do this to a very slight extent, but its 
ability along this line certainly would be very limited, for 
the effect of the movement would probably be diffused 
more or less all over the organism, since there would be no 
part specialized for the purpose of keeping a record. It is 
evident from the citations made above that Loeb regards 
the associative memory as a peculiarity of the central 
nervous system, so that the learning it involves must be of a 
special kind and not merely the plasticity and abiUty to 
modify which characterizes all organic matter. 

Neural Basis of Intelligence 

I believe, therefore, that we are safe in drawing the line 
between intelHgent and unintelligent behavior, between 
conscious and unconscious behavior, between psychic or 
mental and non-psychic behavior at the point where we 
pass from the animals without a central nervous system to 
those with a central nervous system. As we shall see, it 
may be possible to draw this Hne still higher up in the 
evolutionary scale. By this I mean that an animal with- 
out a central nervous system is incapable of intelligent and 
conscious behavior and cannot manifest psychic pheyiomena, 
but that such behavior and phenomena may appear as the 
central nervous system develops. Unless we limit the range 
of intelligence and consciousness, the terms will be meaning- 
less. The reasons for drawing the Hne at the point named 
will appear as we trace briefly the evolution of intelligence 
and consciousness. 



The Nature of Intelligence 263 

In preceding chapters has been shown briefly the part 
played by the nervous system in the behavior of the higher 
animals. It has been shown that, broadly speaking, the 
function of the nervous system is to integrate the move- 
ments of the organism. This is accomphshed by the simple 
and the compound reflexes which are inherited. When a 
combination of these reflexes causes an external movement, 
it constitutes an instinct. These reflex and instinctive 
actions are usually adaptive, for natural selection has been 
at work preserving those individuals which display useful 
inherited reactions. Such adaptation is therefore racial. 
But as we go higher in the animal scale we find usually 
more and more capacity for individual adaptation, and some 
of these adaptations constitute intelhgent behavior. 

The inherited reactions are more or less fiixed at birth, so 
that the parts of the nervous system which determine these 
reactions are already specialized for these purposes at 
birth. In order, therefore, that it be possible for adapta- 
tions to take place, there must be parts of the nervous 
system which are not specialized at birth. We find the 
principal example of such unspeciaHzed nerve tissue in the 
cerebral cortex or gray matter of the brain. It is therefore 
reasonable to suppose that intelligence will vary in accord- 
ance with the amount of gray matter. As we have seen, 
such is the case, and inteUigence is very directly propor- 
tioned to the amount of gray matter in proportion to the 
total size of the body. The amount of the gray matter is, 
as we have seen, determined in the main by the size of the 
cerebrum and by the number of convolutions in the cerebral 
cortex. In this unspeciaHzed nerve tissue, association paths 
become established which correlate the inherited modes of 



264 The Science of Human Behavior 

action into new combinations which constitute new forms of 
behavior which we may call intelligent. This is what leads 
Herrick to speak of the intelligence as the function of the 
cerebral cortex. "In the broad view we may say that in- 
telligence is a function of the cerebral cortex, but only in 
the sense that here are found the most complex correlations 
in the chain of vital response whose initial phase is to be 
sought in the environment which supplies the stimulus and 
whose final phase is also found in the changes wrought in 
the environment by the bodily reaction. '^ ^ 

Let us then discuss briefly the evolution of intelHgence. 
The preceding chapters have shown that every animal 
starts out with an equipment of inherited reactions. The 
forces of the environment are constantly at work upon the 
animal, causing these reactions to vary somewhat, reen- 
forcing some of them, inhibiting others of them. But 
these variations are not necessarily intelligent. The cumu- 
lative efifect of some of these forces may cause changes in 
the structure of the animal which will cause permanent 
changes in its behavior. These permanent changes are 
rudimentary forms of habit and of learning. I have de- 
scribed instances of these in the chapters on the behavior 
of the lower animals. But these lower animals do not 
possess, so to speak, a special mechanism for recording the 
effects of past stimuH, so that these effects may be more or 
less faithfully reproduced in the future by new stimuli 
which may be similar or entirely different from the original 
stimuli. Such a mechanism appears in the form of the 
central nervous system so that as soon as this system begins 

* C. J. Herrick, The Evolution of Intelligence and its Organs, in Science, Vol. XXXI, 
No. 784 Jan. 7, 1910). 



The Nature of Intelligence 265 

to develop, intelligent behavior may become possible. Let 
us see why this is the case. 

The central nervous system is specially adapted for re- 
cording the effects of stimuli. The association areas of 
the cerebrum act as the special organ of memory. It goes 
without saying that a rudimentary form of memory exists 
without this organ because of the plasticity of all organic 
matter, which we have already noted. But this organ re- 
tains an unusually clear-cut and well-defined record of 
these effects. But if this was all that this organ accom- 
plished, intelligence would not be possible, for these effects 
would be reproduced only under the same circumstances 
as when they were first produced. Within the central 
nervous system these effects are connected with other 
sense organs than the ones from which they first originated 
and with other motor organs than the ones through which 
they were originally discharged. This is why the kind of 
memory which is based upon the central nervous system 
is spoken of as associative memory. These memories do 
not stand alone by themselves, but become intimately in- 
terrelated in a very complex fashion. So it is that in an 
animal with a well-developed central nervous system which 
has acquired a large and varied store of memories, the behavior 
which results from a certain stimulus may he vastly different 
from the purely inherited reaction which would respond to that 
stimulus if these memories were not present to vary and com- 
plicate the behavior. Such behavior is intelligent , and the ca- 
pacity for such variations in behavior constitutes intelligence. 

A central nervous system is then a sine qua non for in- 
telligence. But intelligent behavior will not appear neces- 
sarily as soon as the central nervous system. In fact, this 



^66 The Science of Human Behavior 

organ must develop considerably before such behavior is 
possible. Furthermore, the inherited modes of reaction 
probably must be relatively modifiable before intelUgence 
can make its appearance. It is doubtful if simple reflexes 
or compound reflexes which cannot be called instincts can 
furnish the basis for intelHgent behavior. A sufficient 
number of instincts which are readily modifiable is neces- 
sary before there can be variations in behavior which can 
be called intelligent. This fact alone indicates that in- 
telligence is not possible until the central nervous system 
has developed considerably. According to the definition 
which I formulated in an earlier chapter, an instinct is an 
integration and correlation of reflexes by the central nerv- 
ous system. This kind of integration and correlation is 
inherited and is performed by the sensory and motor parts 
of the central nervous system, which are speciahzed for 
these purposes. When a certain number of these instincts 
which are relatively modifiable have evolved, and when the cen- 
tral nervous system has developed parts which are not special- 
ized at birth, so that they can serve as association areas, then 
intelligence may make its appearance} 

* In view of the present-day vogue of the Bergsonian philosophy I feel it neces- 
sary to call attention to the ideas of this philosopher with regard to the relation be- 
tween instinct and intelligence. According to Bergson the ability of the intellect to 
acquire knowledge is very limited, and with respect to life and living things in par- 
ticular instinct in a sublimated form which he calls "intuition " is much more ca- 
pable of acquiring knowledge. In view of our previous discussion of instinct and in- 
telligence it is manifestly absurd to speak of the acquiring of knowledge by instinct. 
It is true enough that the capacity of the intellect to learn is very limited, but un- 
fortunately it is the only means of acquiring knowledge. It is also true that from 
instinctive actions and from feelings, which Bergson confuses with instinct by iden- 
tifying it with sympathy, the intellect learns a great deal. It is true enough that 
the intellect is unable to comprehend life as a whole with one all-seeing glance and 
has to look at it piece by piece, so to speak, but mankind will not come any nearer 
to attaining this end by means of the mythical Bergsnnian " intuition." 

It is unfortunate that Monsieur Bergson, who is so well acquainted with modem 



The Nature of Intelligence 267 

Many experiments have been made upon many kinds 
of animals to determine whether they displayed intel- 
ligence. Unfortunately I have not the space to sum- 
marize these experiments here, interesting though it would 
be to do so. In many of these experiments it has been im- 
possible to determine whether variations which were ob- 
served in behavior were intelligent or not. It may well 
be that it will never be possible to determine exactly at 
what point along the different lines of organic evolution 
the transition took place from unintelligent to intelligent 
behavior. This is to be expected in view of the continuity 
in the evolution of behavior. Because of this continuity, 
the transition would probably be gradual usually, and would 
usually if not always be imperceptible. It is nevertheless 
useful to define intelligence as we have been doing in order 
to distinguish broadly between the different types of be- 
havior, even though we may not be able to tell in every case 
whether or not it is present. Furthermore, it is possible 
to tell in the great majority of species whether or not in- 
telligent behavior is manifested. 

Distribution of Intelligence 

It is probable that intelHgence has appeared along sev- 
eral divergent lines of evolution whenever the requisite con- 
biology and has so brilliantly restated the ancient conception of evolution as a pro- 
cess flowing without a break, should attempt to exalt this " intuition " over intellect, 
however weak iatellect may be. If we take Bergson's statement literally, this "in- 
tuition " is made up of instinct and sympathy and therefore consists of tendencies 
to acting and feeling, but not to thinking and knowing. However, it is probable that 
the phenomena which he has in mind and vaguely describes tmder the name of " in- 
tuition " in reality constitute an intellectual process and should be recognized as 
such. But like every intellectual process it derives much of its data from instinctive 
actions and states of feeling. I have not the space here to describe what this pro- 
cess is. 



268 The Science of Human Behavior 

ditions described above have been fulfilled. Loeb says that 
it ^'can be shown that Infusoria, Coelenterates, and worms 
do not possess a trace of associative memory," ^ and there- 
fore no intelligence. 2 He goes on to say that certain in- 
sects, such as wasps, have been shown to display intelli- 
gence. Experiments made by Yerkes on the crayfish, and 
other similar experiments, have indicated that crustaceans 
may possibly display faint glimmerings of intelligence, 
though it is rather doubtful. Numerous experiments have 
been made upon insects, which seem to indicate that 
intelligence appears occasionally among these animals. 
Among these experiments might be mentioned those of 
Forel, Wasmann, and Wheeler on ants, those of Lubbock 
and the Peckhams on wasps, and those of Lubbock and 
others on bees. It may be, however, that the presence of 
intelligence among the invertebrates is not certain. But 
when we turn to the vertebrates, we find certain evidence 
of its presence in all the higher vertebrates, while it may 
also exist to a slight extent among the lower vertebrates. 
Thorndike seems to have found evidence of it in fishes and 
Yerkes in reptiles. There is much more evidence of its 
presence in birds, while the evidence of its presence in all 
the mammals is probably complete.' 

As has been said before, the transition from unintel- 
ligent to intelligent behavior has probably taken place 

J op. cii., p. 13. 

' "Le pouvoir associatif a subi un premier perfectionnement chez les cnistac6s et 
les insectes, grace au perfectionnement des organes des sens, et surtout de Tceil, 
c'est-k-dire des appareils recepteurs ; il a subi un second perfectionnement chez les 
vert6br6s, grace au d^veloppement des centres nerveux, c'est-a-dire des appareils 
enregistreurs." (G. Bohn, La naissance de V intelligence, Paris, 1910, p. 342.) 

' Since this chapter was written S. J. Holmes' The Evolution of Animal Intel- 
ligence (New York, 191 1) has been published, which contains numerous illustra- 
tions of the presence of intelligence in different parts of the animal world. 



The Nature of Intelligence 269 

several, perhaps many, times along divergent lines of evolu- 
tion whenever the requisite conditions were fulfilled. But 
the structural basis or action-system has been such in most 
of these cases as to prevent great development of intelH- 
gent behavior. This has been true of the insects. In 
them inherited modes of action in the form of reflexes and 
instincts have been carried to a high pitch of perfection. 
But in them, as in all the invertebrates, the action-system 
has apparently made possible only to a very slight extent, 
if at all, the individual modifications which constitute in- 
telligent behavior. 

But the structure, and therefore the action-system, of the 
vertebrates has been such as to make possible an extended 
development of these individual modifications in behavior. 
These characteristics of the vertebrates have been de- 
scribed, so that I need to refer to them only briefly here. 
The skeleton or bony structure which gives the necessary 
rigidity to the organism is in the case of the vertebrate on 
the inside, while in the invertebrate it is on the outside. 
This gives, generally speaking, more freedom of movement 
to the vertebrate, which can bend more easily and place it- 
self in a greater variety of positions than the invertebrate. 
Furthermore, most of the exterior of the vertebrate is 
covered with sensitive tissue which enables it to receive 
many more impressions than the invertebrate, much of 
whose exterior is covered with a hard, insensitive tissue. 

The vertebrate is arranged upon the general plan of a 
s&ries of segments which are characterized by bilateral 
symmetry. In an organism so arranged the anterior seg- 
ments, which habitually go first when the animal is in 
movement, receive many more impressions than the other 



270 The Science of Human Behavior 

segments. Thus the head and brain gain the enormous 
development which characterizes the vertebrate head and 
brain, and gives them their ascendancy in directing the 
behavior of the animal. The cerebrum, which, as we have 
seen, is the organ of intelligence, probably received most 
of its development from the impressions received through 
the sense organs in the head. ''We owe to the genius of 
Edinger the suggestion that the earliest stages in the origin of 
the pecuUarities of the cerebral hemispheres must be sought 
in a study of the character of the reflexes connected with 
the nose and lips, particularly the feeding reactions. These 
have been termed collectively the 'oral sense' (Edinger) 
or ^ Schnilffelsinn^ (Kappers) and may perhaps best be 
called the muzzle reflexes." ^ 

Human Intelligence 

These reasons for the development of the cerebrum have 
been peculiarly true in the case of man and the pre-human 
ancestors of man, and in this fact We can probably find the 
explanation for man's superior intellectual development. 
But not only the nose and hps have played a part in this 
development, but the arms and hands as well. Let us see 
how this development in all probability took place. I 
have already shown that intellect results from the associa- 
tions estabhshed in the association areas of the cerebral 
cortex. Flechsig has shown that these areas constitute 
fully two thirds of the cerebral cortex in the human brain, 
a greater proportion than in any other animal. The prob- 
lem is how man acquired so much association area. In 
the first place, in order to have more association area, the 

^ C. J. Herrick, op. cit., p. 14, 



The Nature of Intelligence 271 

bulk of the cerebrum must be greater, and this means a 
larger cranium. Whether it was the pressure of a growing 
brain which forced the cranium to expand, or some other 
force, it is hard to determine, but it is quite Hkely that owing 
to the sutures which knit together the cranial bones, the 
cranium was able and did respond to the pressure of a 
growing brain. At any rate, since the primate type of 
mammal began to evolve, the cranium has expanded 
greatly, thus leaving room for the larger brain. 

Flechsig, Johnston, and others have shown that the 
higher association centers are on the frontal and parietal 
convolutions of the cerebral cortex. Cunningham has 
summed up his theory as to the causes for the great ex- 
pansion of these cortical areas in man in the following 
words: ''I do not think that it is difficult to account 
for this important expansion of the cerebral surface. In 
the fore part of the region involved are placed the groups 
of motor centers which control the muscular movements 
of the more important parts of the body. These occupy 
a broad strip of the surface which stretches across the whole 
depth of the district concerned. Within this are the cen- 
ters for the arm and hand, for the face, the mouth, and the 
throat, and Hkewise, to some extent, the center for speech. 
In man certain of these have undoubtedly undergone marked 
expansion. The skilled movements of the hands, as shown 
in the use of tools, in writing, and so on, have not been ac- 
quired without an increase in the brain mechanism by which 
these are guided. So important, indeed, is the part played 
by the human hand as an agent of the mind, and so per- 
fectly is it adjusted with reference to this office, that there 
are many who think that the first great start which man ob- 



272 The Science of Human Behavior 

tained on the path which has led to his higher development 
was given by the setting of the upper limb free from the 
duty of acting as an organ of support and locomotion. . . . 
In the same region of cerebral cortex, but at a lower level, 
there are also situated the centers which are responsible 
for facial expression." ^ 

Presumably, then, it was great stimulation of these motor 
centers for the arms, hands, face, and mouth which also 
stimulated the growth of the contiguous association areas. 
The next question would then be as to what caused this 
large amount of stimulation of these motor centers. It is 
of course impossible to ^reconstruct entirely the history of 
man's ancestors, but we can make some plausible conjec- 
tures as to its course. We have good reason to beheve that 
the early primates were arboreal in their habits, as indeed 
is still true of most of the primates. It was probably the 
development of fruit on the late mesozoic or early tertiary 
trees which led to the habit of climbing.^ This habit 
naturally stimulated greatly the motor centers for the hands 
and arms. Just why some of the primates later on aban- 
doned the trees and adopted terrestrial habits, now walking 
in a partially erect attitude, it is not easy to explain. But 
the fact that this change took place is certain, and some 
of the results from it can easily be conjectured. With its 
hands off the ground they could be used for finer adaptations 
than ever before, such as hurling missiles and later for 
using tools. On the ground it would be exposed to more 
dangers than in the trees. Vision and hearing would be 
used more than ever, and would consequently be greatly 

^ D. J. Cunningham, in Nature, Sept. 26, 1901. 

• C£. Joseph McCabe, The Evolution oj Mind, London, 1910, p. 257. 



The Nature of Intelligence 273 

strengthened and would furnish much material for the 
intelKgence. In the face of dangers which these primates 
were not able to overcome by force because of the superior 
strength of many of the animals which preyed upon them, 
the more intelligent, which would therefore be the more 
wary and cunning, would be preserved, so that selection 
would be at work favoring the development of intelligence. 
In order to indicate all the factors which played a part in 
the development of man's superior intelHgence, it would be 
necessary to review the whole course of man's early physical 
and mental evolution, which there is not the space to do 
here. Enough suggestions have been made to indicate 
how it may have taken place. It goes without saying that 
all that has been said so far has to do only with the evolu- 
tion of the cerebral basis for intelligence. Much of the 
contents of the mind is passed on from generation to genera- 
tion by education and tradition, so that it is not hereditary. 
But in order that this knowledge may be acquired and then 
transmitted from generation to generation, a certain cerebral 
basis is necessary. 

Nature of Learning 

I have now discussed briefly the nature of intelligence, 
the extent to which it prevails in the animal world, and the 
causes of the superiority of human intelligence. I shall 
now discuss a Httle further the nature of learning and the 
higher forms of intelligence. This will lead naturally to 
the discussion of consciousness, since it is impossible to dis- 
cuss these higher forms apart from consciousness. 

It has been shown earlier in this chapter that in one 
sense all organisms are capable of learning. That is to 



274 The Science of Human Behavior 

say, because of the plasticity of organic matter the behavior 
of all organisms may be modified by the action of external 
forces. But it is rather absurd to call this learning. For 
example, to say that a plant learns is decidedly incongruous. 
In order to give the term utility in distinguishing between 
different types of behavior, / shall limit learning to the modi- 
fications in the behavior oj an animal capable of forming im- 
ages, when such modifications are due to this ability to form 
images. An animal is able to form images when it retains 
a memory of the experiences through which it passes. Here 
again it is necessary to limit the meaning of the word mem- 
ory. It is contended by some that all organisms have 
memory because of the great plasticity of organic matter. 
But I believe that it is better to restrict the use of the term 
to the abihty to reproduce or reconstruct in some fashion 
an experience through which the animal has passed. This 
does not result from the general plasticity of protoplasm, 
which cannot reproduce the experience through which it 
passes, though it may be modified by it. For memory to 
exist, a special organ of memory is needed, and this organ 
is to be found in the association areas of the cerebrum. 
As we have seen, impressions received through the senses 
are recorded upon these areas, so that later on when these 
areas are again stimulated the sensations will again be re- 
vived in part, if not in full, without the original causes of 
the sensation being present. 

The process of learning, then, consists in part in forming 
these images of sensations experienced. It is evident that 
these images must influence behavior. If an image is of 
a sensation which gave rise to an act, it will be connected 
with the motor impulse which went to the motor organ. 



The Nature of Intelligence 275 

When, therefore, this image is stimulated in the future, it 
may in turn stimulate the motor center, which will send an 
impulse to the motor organ and thus give rise to the same 
act. This is ideo-motor action, which follows upon an image 
and not upon a stimulus from without, as is the case in 
sensori-motor action. It is evident that ideo-motor action 
is possible only to animals that can form images, so that 
the whole range of ideo-motor action is pecuUar to these 
animals. 

But the act connected with an image will not necessarily 
follow when that image is aroused. That will depend in 
part upon what has been the result of that act in the past. 
If the effect of the act has been pleasing, the path from the 
motor center to the end organ will be reenforced, so to speak, 
so that the act is more Hkely to be repeated. If the effect 
of the act has not been pleasant, the pathway to the end 
organ will be weakened or blocked, so that the act is not so 
likely to be repeated. This brings us to the phenomena 
of pain and pleasure which play so important a part in 
the determination of the behavior of the higher animals. 
The problem of the nature of pain and pleasure is closely 
connected with that of consciousness, so that it will be dis- 
cussed in connection with consciousness. I will say here, 
however, that these phenomena seem to be characteristic 
of nervous matter and are apparently never experienced 
apart from such matter. Presumably they arise out of 
the states of the neurones involved. If the effect of a cer- 
tain act upon the states of the neurones involved is harmful, 
the pathway to the end organ which caused that act will 
probably be weakened so that the act is not so likely to 
take place again. This weakening will probably be by a 



276 The Science of Human Behavior 

weakening of the synapses between the neurones along 
the pathway to the end organ. But we do not yet know 
enough about the inherent nature of the nervous system to 
understand just how and why these reenforcements and 
inhibitions of acts take place in the nervous system. If 
we did know, we would understand much better how these 
modifications in behavior which constitute intelligence 
come about. As Thorndike has said: ''We may, there- 
fore, expect that when knowledge of the structure and be- 
havior of the neurones comprising the connection-systems 
of animals (or of the neurones' predecessors in this function) 
progresses far enough to inform us of just what happens 
when a connection is made stronger or weaker and of just 
what effects satisfying and annoying states of affairs exert 
upon the connection-system (and in particular upon the 
connections most recently in activity) the ability to learn 
will show as true an evolution as the ability to sneeze, 
oppose the thumb, or clasp an object touched by the 
hand." 1 

We can now see that the process of learning includes the 
strengthening and weakening of associations as well as the 
formation of images. These two factors alone will intro- 
duce a large amount of uncertainty into the behavior of 
the animal. The observer of its behavior cannot know 
what images are recorded in its brain. Nor can he know 
all the pleasurable and painful feelings it has experienced 
and the associations which have been established by them. 
And yet a complete knowledge of both these things as well 
as a knowledge of the inborn tendencies to action of the 
animal is necessary to explain its behavior. 

* E. L. Thomdike, Animal Intelligence, New York, 191 1, p. 280. 



The Nature of Intelligence 277 

The Forms of Intelligence 

These two factors are probably all that play a part in 
the intelligent behavior of all but a few of the higher animals. 
But in these higher animals these processes become much 
more complex, thus making much more uncertain the be- 
havior of the animal. As the association areas grow and 
the radiation of association fibers becomes more refined, 
these images become related to each other in a very complex 
fashion. Thus there arise the higher forms of intelligence. 
The first of these is the idea. This term is used in some- 
what different ways. Frequently it is used in such a 
fashion as to imply a high order of intelligence, as when 
"a man of ideas" is spoken of. But the more technical 
psychological meaning is much broader, as indicated in 
Baldwin's Dictionary, which defines an idea as being "the 
reproduction, with a more or less adequate image, of an 
object not actually present to the senses." It is evident 
that according to this definition an idea is little if anything 
more than an image, though sometimes an idea may be 
formed by the association together of several images. 
Ideas therefore may be held by animals which have not 
yet attained a very high grade of intelligence. 

Thought is the next higher form of intelligence. It is 
not, however, a distinct thing in itself, but is simply the 
name for a flow of ideas, so to speak, which do not neces- 
sarily give rise to any external action. That is to say, an 
idea stimulates another idea and that one still another one, 
and so on, by means of the connections between their nerve 
centers in the associative tracts of the cerebrum, so that 
thinking is the name given to the mental process which is 



278 The Science of Human Behavior 

the result from or the concomitant, as the psycho-physical 
parallelists say, of this cerebral process. In order to have 
thought, therefore, it is necessary to have a large supply of 
ideas which are much interrelated. A higher grade of 
thought is conceptual thought in which concepts constitute 
the flow of thinking. A concept is a generalized image of a 
characteristic common to a number of images. It is evi- 
dent that according to these definitions thought is made up 
of images. Introspection on the part of most people re- 
veals images at the basis of all ideas and of all thinking. 
These images may be visual, auditory, tactile, kinaesthetic, 
etc., according to the nature of the sensations they repro- 
duce. The introspective method is of great value at this 
point as throwing light upon the origin and nature of these 
phenomena. 

Strange to say, however, there are a number of psycholo- 
gists who have recently claimed the existence of imageless 
thought. Among them are to be found such writers as 
Stout, Binet, Woodworth, Buhler, etc. Their claims have, 
however, aroused much opposition among other psycholo- 
gists, and a bitter controversy is now raging over this ques- 
tion. Already replies have been made to the supporters 
of imageless thought by Wundt, Titchener, Angell, etc., 
and it is probable that more criticism of their ideas will be 
forthcoming soon. There is not the space to review this 
subject fully in this place, so that I shall be able to make 
only a few comments. 

The advocates of imageless thought seem to have in- 
trospective evidence of the existence of such thought. It 
is true that some of the subjects of their investigations 
have claimed to have had ideas and other forms of tliink- 



The Nature of Intelligence 279 

ing independent of imagery. It is also true that some of 
these subjects have been trained psychologists. But error 
and self-deception are possible, even in the case of the 
trained subject. It may even happen sometimes that the 
trained subject is more likely to be deceived than the un- 
trained one, for he is more Hkely to be looking for something 
in his mental processes, and may therefore deceive himself 
into thinking that he has found what he was looking for. 
This may explain why some of these trained subjects 
thought they experienced imageless thought. In any case 
it is well to bear in mind that mistakes may be made in 
introspection, even by trained observers. It is evident that 
imageless thought is quite contrary to the fundamental 
principles of modern psychology, so that very weighty evi- 
dence in its favor must be found before it can be accepted 
generally by psychologists. In the meantime we are safe 
in assuming that all thinking is done in images. 

The highest form of intelligence is reason^ which Baldwin's 
Dictionary defines as being ^'that faculty and process of 
mind which consists in the drawing of inferences." A 
large store of ideas is necessary for the appearance of reason. 
Then in the course of the flow of thought from one idea to 
another, similarities and differences between them will be 
recognized or other relations established which constitute 
reasoning. As I have already indicated, many have thought 
that reason is peculiar to man. If it is meant by this that 
there is not continuity in mental development from the 
lower animals to man, then reason cannot be regarded as 
peculiar to man in that sense. But if it is meant that no 
other animal has a sufficiently large store of ideas to fur- 
nish material for reason, then it may be that reason is to 
that extent peculiar to man. 



280 The Science of Human Behavior 

It may then be that man is the only animal that possesses 
reason, and the same is in large part true of the other higher 
forms of intelligence. I have already discussed briefly 
how the evolution of man's superior intelligence can be 
traced up through the lower mammals and the primates 
to man. We have seen that it is due in part to the supe- 
riority of certain of his senses which are of peculiar value in 
acquainting him with his environment, inasmuch as they are 
the functions of distance-receptors. It is due in part to his 
action-system, which enables him to go through an unusually 
varied number of movements. It is due in the last place to 
his extended association areas, which furnish the basis for an 
unusually extensive and complicated system of connections 
between sensations, images, and movements. It is interesting 
to observe how the monkeys and the anthropoid apes mark 
the development and the transition along all these lines 
from the lower mammals to man.^ 

But, as has been said, it is impossible to discuss fully 
the higher forms of intelligence apart from consciousness. 
So that I shall now take up the discussion of consciousness. 

1 Thorndike has summed up well the causes of man's superior intelligence in the 
following words: "The pecuHarly human features of intellect and character, 
responses to elements and symbols, are the results of : first, a receiving system that 
is easily stimulated by the external world, bit by bit (as by focaUzed vision and touch 
with the moving hand), as well as in totals composed of various aggregates of these 
bits ; second, of an action-system of great versatility (as in facial expression, artic- 
ulation, and the hands' movements) ; and third, of a connection-system that in- 
cludes the connections roughly denoted by babbling, manipulation, curiosity, and 
satisfaction at activity, bodily or mental, for its own saJce ; that is capable of work- 
ing in great detail, singling out elements of situations and parts of responses ; and that 
allows satisfying and annoying states of afifairs to exert great influence on their 
antecedent connections. Because he learns fast and learns much, in the animal way, 
man seems to learn by intuitions of his own." {Op. cit., p. 281.) 



CHAPTER XV 

consciousness: sensation, attention, feeling, pleas- 
ure, PAIN, AND emotion AS CONSCIOUS ELEMENTS 

Spiritual conceptions of consciousness, 282. — Consciousness as 
characterizing all matter, 283. — Consciousness as characterizing 
all organic matter, 283. — Consciousness as an epiphenomenon, 
287. — Consciousness as associative memory, 288. — The neural 
basis of consciousness, 288. — The relation between intelligence and 
consciousness, 289. — Sensations as the raw material for conscious- 
ness, 290. — The nature of attention, 290. — The nature of feel- 
ing, 291. — Pleasure and pain, 292. — Feelings as pleasurable and 
painful sensations, 292. — The neural basis of feehngs, 292.— 
Feelings of pleasantness and unpleasantness, 298. — The nature of 
emotion, 299. — The visceral and vasomotor origin of emotions, 
300. — Emotions as affective sensations or feelings, 301. 

The term consciousness is closely associated with the 
terms mental and psychic, and it is very difficult to find any 
definitions of these words, which give any concrete idea of 
their meaning. A curious example of this is to be found in 
Baldwin's Dictionary of Psychology and Philosophy in the 
definitions of the words consciousness and mind. In that 
work consciousness is defined as being "the distinctive 
character of whatever may be called mental Hfe." Mind 
is defined as being "the individual's conscious process, to- 
gether with the dispositions and predispositions which 
condition it," In other words, consciousness is defined in 
terms of the mental, while mind is defined in terms of the 
conscious, so that no concrete indication is given of the 

281 



282 The Science of Human Behavior 

meaning of these words, if they have any.^ I shall there- 
fore try to make my own analysis of consciousness on the 
basis of the preceding study of the different forms of be- 
havior. This analysis will be as far as possible objective, 
though a little introspective data will be used. 

Definitions of Consciousness 

It will be impossible to discuss all the different concep- 
tions of consciousness which have been held in the past, 
many of which are still held, but a very brief statement 
will be made of some of the principal ones. Many writers 
in the past and a few still in the present have regarded con- 
sciousness as something spiritual and mystical in its char- 
acter which resides in certain animals or in all living beings. 
Usually these writers have regarded it as a distinct entity 
or category which enters the body at the beginning of life 
and leaves it at death. Such theories are closely related 
to the religious doctrine of the soul and regard conscious- 
ness as something entirely distinct from matter. It is 
hardly necessary to state that no such theory of conscious- 
ness can be regarded as scientific because there can be no 
inductive evidence of the existence of any such spiritual 
entity. Furthermore, it denies the fundamental postulate 
of science that all things must be reduced as far as possible 
to the same terms, and assumes an ultimate duaUsm in the 
universe. 

* This dictionary was written by a considerable number of collaborators ; 90 
that it would not be surprising to find contradictions and such a circular method of 
defining as is illustrated in the definitions quoted above, if the definitions were taken 
from articles written by different persons. But the two articles from which the 
above definitions are quoted, namely, the articles on consciousness and on mind, 
are both of them signed by the same authors, namely, G. F. Stout and J. Mark 
Baldwin. 



Consciousness 283 

On the other hand, there have been those who have 
carried this postulate of science to an absurd extreme by 
trying to prove that consciousness characterizes all matter. 
It is evident that if the term is to mean anything and is to 
be useful in the work of science, which is to describe natural 
phenomena, its application must be Umited somewhat. 
This attempt to prove that all matter is conscious has been 
made by certain monists, and James has contended that 
such monism represents "reality" as having two irredu- 
cible aspects, the conscious and the material, so that it 
results practically in dualism. He goes on to show that 
when consciousness is represented as being fluid, unex- 
tended, diaphanous, and without content, it is a chimera, 
and that the term means nothing unless it includes concrete 
reaHties.^ 

Others have formulated more scientific theories to the 
effect that all organisms are conscious. I will give a few 
examples of such theories. Many of those who have held 
such theories have apparently been influenced principally 
by these two considerations. In the first place, in view of 
the continuity in the development of behavior, there is no 
place where consciousness could suddenly have made its 
appearance, and therefore must have been present at the 
beginning. In the second place, because of the analogies 
which exist between human behavior, which is undoubtedly 
conscious, and the behavior of the lower animals, all behavior 
must be conscious. For example, Jennings seems to have 
been greatly influenced by both of these considerations and 
especially by the second one, so that he is incHned to think 
that the behavior of all organisms is conscious. After 

1 La notion de conscience, in the Archives de psychologies Vol. V. 



284 The Science of Human Behavior 

raising the questions, on the one hand, as to whether the 
behavior of the lower organisms seems to be conscious, or, 
on the other hand, as to whether it seems to be uncon- 
scious, he says : "If one thinks these questions through for 
such an organism as Paramecium, with all its Hmitations of 
sensitiveness and movement, it appears to the writer that 
an affirmative answer must be given to the first of the above 
questions, and a negative one to the second. Suppose that 
this animal were conscious to such an extent as its Hmita- 
tions seem to permit. Suppose that it could feel a certain 
degree of pain when injured ; that it received certain sen- 
sations from alkali, others from acids, others from soHd 
bodies, etc., — would it not be natural for it to act as it 
does? That is, can we not, through our consciousness, 
appreciate its drawing away from things that hurt it, its 
trial of the environment when the conditions are bad, its 
attempting to move forward in various directions, till it 
finds one where the conditions are not bad, and the like ? 
To the writer it seems that we can." ^ 

It is evident that Professor Jennings is drawing analogies 
between the behavior of the lower organisms and the higher 
animals which are probably not justified. For example, 
he thinks that a Paramecium experiences pain when it is 
injured and draws away from harmful things for that reason. 
We have already discussed the mechanism of such behavior, 
using Jennings' own investigations to a large extent as a 
basis, and have seen that it is the result of the action of 
external forces upon the organism, constituting a tropism. 
As I have already stated, and as will be discussed more 
fully later on, pain and pleasure seem to be states that 

1 Behavior oj the Lower Organisms^ New York,' 1906, p. 336. 



Consciousness 285 

characterize the nervous system, so that it is very doubtful 
if they exist in organisms without a nervous system. Here 
again, as we have found to be true elsewhere in his writ- 
ings, Jennings is carrying to an extreme his idea of the con- 
tinuity in behavior and by so doing is destroying the utility 
of the word consciousness. It is evident that if all organ- 
isms are regarded as being conscious, the term means no 
more than sentiency, which is itself a very vague term, 
probably meaning no more than a high degree of plasticity 
arising out of the complex chemical composition of proto- 
plasm. So that if the term is to have any utility in dis- 
tinguishing between the different types of behavior, we 
must limit its meaning somewhat. 

As a matter of fact, the continuity theory proves too much. 
If its upholders refuse to admit that consciousness made 
its appearance in the course of organic evolution, because of 
the continuity in the development of behavior, then why do 
they think that it appeared at the moment of transition 
from the inorganic to the organic ? If they are thorough- 
going evolutionists they must believe that there was no 
absolute break at this point and that therefore there was no 
more reason for consciousness to appear at this point than 
later on. In other words, the logical conclusion of their 
theory would be that all matter is conscious, and this, as 
we have seen, is absurd. 

This idea that consciousness characterizes all life has 
been very widespread and has manifested itself in many 
forms. Some seem to think that it is the essential prin- 
ciple of Hfe. Others think that it is something entirely 
distinct from the life principle, which however it invariably 
accompanies. This is the parallelist theory that mental 



286 The Science of Human Behavior 

and organic processes accompany each other, without, 
however, affecting each other. It may be that some paral- 
lehsts do not believe that mind accompanies all manifes- 
tations of Hfe, but only some of the more complex of these 
manifestations. A curious variant of this theory is that 
the early organic movements were conscious, but on be- 
coming habitual lost their conscious character and were 
inherited as unconscious reflex actions. We have already 
met this theory in an earlier chapter in the lapsed intelH- 
gence theory of instinct held by Lewes and Romanes. 
There seems to be some evidence in favor of this theory in 
the fact that conscious acts may on becoming habitual 
become unconscious and thus simulate the appearance of 
reflexes. But, as we have seen, no such acquired habit 
can be inherited, so that it is absurd to suppose that any 
inherited mode of action could have had a conscious ori- 
gin. A singular illustration of this theory is to be found in 
one writer who tries to show that the movements which ex- 
press emotions in man are inherited from the conscious 
movements of man's ancestors. For example, he says: 
''The face of proud contempt reflexly 'curves a contume- 
lious Up.' What does the movement mean ? Why, it lays 
bare the canine teeth ; it is the human counterpart of the 
snarl of dog or wolf; it is the last reflex or unconscious 
remnant of a coordinated or impulsive action which, 
somewhere or other in our not remote ancestry, preceded 
the movements of actual attack. The deer bounds away 
when it hears the hounds, and we 'jump' when we are 
startled ; the sitting bird crouches on its nest when danger 
approaches, and we wince or shrink when we are frightened 
or censured. . . . Here is evidence of the derivation of 



Consciousness 287 

unconscious from conscious movement, not in the life his- 
tory of the individual, but in that of the race." ^ In view 
of the preceding discussion of instinct, it goes without 
saying that these movements were no less unconscious and 
quite as reflex as they are in the human and other beings 
of to-day. 

There is not the space to discuss at greater length these 
theories of consciousness, but I think that enough has been 
said to show that they are untenable. As has been shown, 
it is contrary to the fundamental postulate of science that 
all phenomena must be reduced as far as possible to the 
same terms to assume that consciousness is anything funda- 
mentally different from anything else in the universe. 
Furthermore, to assume that consciousness is something 
that characterizes all matter is to identify it with energy, 
which is the universal characteristic of matter. In similar 
fashion, to assume that it characterizes all organic matter 
is to identify it with sentiency, so that in both cases the 
term loses its utiHty when it is applied so extensively. We 
must therefore, in the first place, determine if there is any- 
thing which can be distinguished as constituting conscious- 
ness, and, in the second place, must devise an objective, 
concrete criterion for it. 

But before beginning this task I must discuss briefly 
the theory that consciousness is an " epiphenomenon. " 
I beHeve that Huxley was the first to call consciousness 
by this name. I suppose that he meant by it that con- 
sciousness is not quite a phenomenon, but that it is 
something that accompanies certain organic phenomena, 

1 E. B. Titchener, Were the Earliest Organic Movements Conscious or Uncon- 
scious? in the Pop. Set. Mo., Vol. LX, p. 467 (March, 1902). 



288 The Science of Human Behavior 

It is probable that he gave it that name either because he 
did not think that it existed or because he despaired of 
being able to describe it as phenomenon. Now it goes with- 
out saying that science cannot recognize anything apart 
from phenomena, meaning by a phenomenon something 
which appears to the senses, so that either consciousness 
does not exist at all for man or else it exists as a phenomenon. 
So that I shall try to describe it as a phenomenon. 

What, then, is consciousness ? One of the best known 
attempts to define it objectively is the one which identifies 
it with the associative memory. For example, Loeb de- 
fines it as follows: *' Consciousness is only a metaphysical 
term for phenomena which are determined by associative 
memory." ^ We have already seen that many regard 
associative memory as the mark of intelhgence, which fact 
suggests that consciousness and intelhgence may turn out 
to be the same thing, or at any rate that one of them is 
an aspect of the other. This is a possibiHty which I shall 
discuss shortly. 

If consciousness is determined by associative memory, 
then it cannot appear until this memory has appeared. 
We have seen that associative memory is based upon the 
association areas of the central nervous system and that 
these areas have had their greatest development in the 
vertebrates. In the higher invertebrates, such as the artic- 
ulates, the central nervous system is a segmented chain 
of nerve tissue which is dominated by the metamerism of 
the body and in which the reflex arcs of the different seg- 
ments are kept more or less apart by the anatomical structure 

' Comparative Physiology of the Brain arid Comparative Psychology, New York, 
igoo, p. 12. 



Consciousness 289 

of the animal. But in the vertebrate the central nervous 
system becomes an epithelial tube which is imperfectly 
segmented and which contains a continuous column of 
nerve cells and connecting fibers which forms a sort of 
reticulum. This reticular formation is a diffuse correla- 
tion center which relates together all of the reflex arcs. 
The anterior part of this epithelial tube expands into the 
brain, in which there are the special correlation centers or 
suprasegmental apparatuses, as they are sometimes called, 
which determine most of the mental phenomena of the 
higher vertebrates. Consciousness, then, like intelUgence, 
will appear when the appropriate neural basis for associa- 
tive memory has evolved sufficiently. 

It must now be evident that this conception of conscious- 
ness which connects it so closely with the associative mem- 
ory implies that it is a form of behavior or, to say the 
least, a characteristic of certain forms of behavior. This 
idea is suggested in the following definition formulated 
by Herrick: ^'Consciousness is a functional phase of the 
more complex mechanism of those higher nonstereotyped ac- 
tions for which the reflex machinery is inadequate, in much 
the same way that the tropisms of Paramecium and the suck- 
ing reflex of an infant are functional phases of the simple 
inborn neuromuscular mechanisms of these organisms.''^ ^ 
This definition seems to place consciousness in the same 
category with tropisms and reflexes with which we are 
acquainted as forms of behavior. But if this is true, then 
consciousness and intelligence must be identical, for intelli- 
gence is the functional phase of these higher, nonstereo- 

^ C. J. Herrick, The Evolution of IntelUgence and Its Organs, in Science, Vol. 
XXXI, No. 784 (Jan. 7, 1910). 

U 



290 The Science of Human Behavior 

typed actions. As a matter of fact, the relation between 
the two is very close, and they are undoubtedly at least 
partially identical. But it is not certain that they are 
wholly identical, and it may be that each includes phenom- 
ena which do not belong to the other. I have described 
briefly intelligent phenomena and will now discuss the 
contents of consciousness. After doing so, it will be pos- 
sible to determine to what extent they are identical. 

Sensations and Attention 

We have seen that sensations are the impressions made 
upon the nervous system by stimuli which are received 
through the sense organs. It must be evident that there 
can be no consciousness without sensations. As Spencer 
pointed out, they furnish the raw material for consciousness. 
But sensations do not necessarily involve consciousness. 
If these sense impressions do not reach the higher nerve 
centers so that the acts which result from them are sensori- 
motor, it is inconceivable in view of what has been said that 
they are accompanied by consciousness. But if they do 
reach the higher nerve centers they may become conscious. 
In order to become so, they must be connected iii the asso- 
ciation areas with the images of the same or of other sen- 
sations. However, this alone may not be sufl&cient to 
render the sensations in question conscious. If other sensa- 
tions are being received at the same time, it may be neces- 
sary for attention to be centered upon these sensations in 
order to make them conscious. By attention I simply 
mean that the nervous system responds to certain sensations, 
to the total or partial conclusion of other sensations which are 
being received at the same time. Now this may be due to 



Consciousness 291 

several causes. It may be due to the fact that certain 
sensations are much more powerful than the others being 
received at the same time. Or it may be due to the fact 
that these sensations, though weak as compared with the 
other sensations being received at the same time, are con- 
nected with images which are sufficiently numerous or 
sufficiently vivid to monopolize wholly or in part the capac- 
ity of the nervous system for responding. 

Is then the concentration of attention upon certain sen- 
sations an indication of the presence of consciousness? 
Some psychologists seem to think so. It has been indi- 
cated that Jennings believes that attention in the lower 
organisms is an indication that they are conscious. It is 
true that these organisms will attend to certain stimuli 
to the neglect of others which are acting upon them at the 
same time. This is due either to the fact that these stimuli 
are stronger than the others or to the fact that they have 
acquired the habit of responding to these stimuH. But 
this does not involve the presence of images and ideas as 
in the higher animals, and it is practically certain that this 
sort of attention cannot be regarded as any indication of 
the presence of consciousness. Hence it is that attention 
is not necessarily an indication of the presence of conscious- 
ness, unless we Hmit the term attention to concentration 
which involves a complex combination of images and ideas. 

Pleasure and Pain 

The next element in the contents of consciousness is 
feeHng. This is an exceedingly difficult subject to discuss, 
since there is still great difference of opinion among the 
psychologists as to the nature of feeling. But I think this 



292 The Science of Human Behavior 

much may be safely said to start with, that in all probability 
feelings fall into two main classes, namely, pleasurable 
and painful sensations. Feelings which seem to belong 
to neither of these classes appear so because they are very 
close to the borderline between the two. Assuming, then, 
that all feehngs are either pleasurable or painful, the prob- 
lem of the nature of feeHng reduces itself to the problem 
of the nature of pleasure and pain. 

There have been numerous theories as to the nature of 
pleasure and pain. Most of them have taken account of 
the fact that pleasurable acts are usually beneficial to the 
organism, while painful acts are usually harmful. This 
fact indicates that selection has been at work preserving 
the pleasurable acts and feehngs and eUminating the pain- 
ful acts and feelings. But it is still very uncertain as 
to what is the exact mechanism of pleasure and pain. 
As has been stated, these feehngs are never experienced 
apart from the nervous system, so that we have reason to 
beUeve that their mechanism is nervous in its character. 
Evidence of this is to be found in the fact that in the higher 
animals which display these feehngs they can never be 
stimulated in those parts of the organism which do not 
contain nerve fibers. For example, however much the 
hair, the nails, and other bony parts of the body are in- 
jured, no feehng of pain can be aroused. 

Furthermore, there is reason to beheve that these feel- 
ings do not appear until the nervous system has reached 
a relatively high stage of development. We have evidence 
that the species which do not possess a highly developed 
central nervous system do not display these feehngs, or 
display them only to a shght extent. Norman has gath- 



Consciousness 293 

ered together numerous examples which indicate that such 
is the case.^ For example, if an earthworm is cut in halves, 
only the posterior half squirms and jerks as if in pain. The 
anterior half crawls away as if nothing had happened. 
And yet this is the half which contains the brain, which, 
as the highest part of the nervous system, should be most 
sensitive to painful stimuli. Furthermore, if the two 
halves are subdivided, it again happens in each case that 
the anterior part crawls away, while the posterior part 
squirms and jerks. The same thing happens as frequently 
as the parts are subdivided. It appears then that the 
squirming and jerking of the posterior pieces cannot be 
due to pain, for if this were the case these movements would 
be exhibited as much by the anterior pieces. It is probable 
that the difference in the movements of the two parts is 
due to the fact that when the impulse from the injured 
spot travels forward it affects the circular muscles first, 
thus causing them to contract and the part to elongate 
and to move forward, while when the impulse from the 
injured spot travels backward it affects the longitudinal 
muscles, thus causing the part to squirm and jerk. 

The same phenomenon takes place when the worm Nereis 
is divided. When certain worms such as the Cerebratulus, 
Thysanozoon and Planaria torva, and the leech are divided, 
the posterior half in each case ceases movement, while the 
anterior half moves forward as if nothing had happened. 
Among the echinodermata the starfish and the brittle star 
can be cut to pieces without giving any appreciable re- 
action. Among the Crustacea the legs and abdomen of the 

* W. W. Norman, Do the Reactions of the Lower Animals Against Injury Indicate 
Pain Sensations? in the Am. Jour, of Physiology, Vol. Ill, No. 6 (Jan., igoo). 



294 The Science of Human Behavior 

hermit crab, the spider crab, etc., can be cut away with- 
out any movements which signify pain. Among insects 
the abdomen of bees, dragon flies, etc., has been cut away 
while the creature was eating without disturbing the pro- 
cess of nutrition, which seemed to indicate that there was 
no pain, or that the pain was so slight as not to interfere 
with the nutritive process. Among vertebrates vivisec- 
tion experiments upon fishes such as sharks, flounders, 
etc., have not produced reactions which seemed to indicate 
pain.^ 

It goes without saying that pleasure and pain are phe- 
nomena which can be observed directly only by means of 
introspection. But in this respect they are Hke all other 
mental and psychic phenomena, for all such phenomena 
can be observed directly only by introspection. It is 
possible to judge the mental and psychic phenomena of 
others only by inference. When we see behavior in others 
which is in us the accompaniment of certain mental and 
psychic phenomena, we assume that these others are experi- 
encing the same mental and psychic phenomena. In this 
fashion we can judge as to manifestation of pain and pleas- 
ure by other species. If when injured they do not manifest 
any reactions at all, or do not manifest the sort of reactions 
which we give when pained, we have some reason to believe 
that they are incapable of experiencing painful feelings. 
To be sure, this is not a sure sign, for it may be that the 
reactions in other species may be very different from what 
they are in man. But in the cases cited above, either no 

* Cf. W. W. Norman, Do the Reactions of Lower Animals Due to Injury Indicate 
Pain-Sensations? in Biological Lectures from the Wood's HoU Marine Biological 
Laboratory, Boston, iSgg; also in PflUger's Archiv, Bd. LXVII, p. 137; Loeb, op. 
cit., pp. 229-232 ; W. M. Wheeler, Ants, New York, 1910, p. 509. 



Consciousness 295 

reactions whatever were given when injury was inflicted, 
or else the reactions were of such a nature as could be fully 
explained on other grounds than as manifestations of pain- 
ful feehngs. When, however, we come to the higher verte- 
brates, and especially the mammals, we find unmistakable 
evidence of pleasurable and painful feelings. These are 
movements of drawing away from painful stimuK and ap- 
proaching pleasurable stimuli, the utterance of cries and 
other sounds, the expression of the face in some of the higher 
animals, etc. 

Feeling is then apparently limited to animals with a cen- 
tral nervous system which is quite highly developed. As has 
been indicated, there have been many theories as to the 
mechanism of feeling. Spencer propounded the theory 
that pleasure is the concomitant of heightened nervous 
discharge, while pain is the concomitant of lessened nervous 
discharge. Later, Bain and Baldwin proposed similar 
theories as to the physiology of pleasurable and painful 
feehngs. According to these theories, pleasurable acts are 
more likely to be repeated, because the heightened nerv- 
ous discharge which has accompanied them has opened 
up the paths to the motor organs involved and has reen- 
forced the tendency to perform these acts. Painful acts 
are less likely to be repeated, because the lessened nervous 
discharge which has accompanied them has, to say the 
least, not opened up the paths to the motor organs involved, 
while it may even have an inhibitory effect upon them. 
But it is doubtful if these theories are correct, for it seems 
quite evident that painful acts are accompanied by as 
heightened a nervous discharge as pleasurable acts fre- 
quently, if not always. Certainly the vigorous reactions 



296 The Science of Human Behavior 

usually given to painful feelings would seem to indicate 
that such is the case. Furthermore, if this theory were 
true, it would be reasonable to suppose that pleasure and 
pain would arise very low in the animal scale, for there 
could be this difference in the strength of the nervous dis- 
charge as soon as there were any nervous currents. To be 
sure, it is not absolutely certain that pleasurable and pain- 
ful feelings are not experienced very low in the animal 
scale, but I have given reasons for believing that such is 
not the case. 

Another theory is that painful feelings are caused by 
special organs for pain. That is to say, certain nerve fibers 
are specialized for the purpose of giving warning against 
harmful stimuli, and the sensations received through these 
organs are those which we call painful feeHngs. These 
special organs for pain are distributed throughout the or- 
ganism according to need. Those who hold this theory 
usually believe that pleasurable feeHngs are diffused forms 
of sexual sensations. According to this theory it is easier 
to believe that painful and pleasurable feelings do not 
appear until relatively high in the organic scale, at least 
so far as painful feelings are concerned, for these feelings 
could not appear until the appropriate organs for them had 
developed. According to this theory it is also possible to 
believe that one kind of feeling appeared before the other, 
and there is some reason for believing that painful feelings 
appeared before pleasurable feelings. 

Feelings 

But feelings have not been studied enough as yet to 
furnish a well-established theory as to their nature. Cer- 



Consciousness 297 

tainly nothing definite can be learned from what are sup-, 
posed to be authoritative sources of information. For 
example, Baldwin's Dictionary defines feeling as being "con- 
sciousness as experiencing modifications abstracted from 
(i) the determination of objects, and (2) the determination 
of action." ^ This definition is utterly meaningless to me, 
with the exception that it is apparently defining feehng in 
terms of consciousness. As we have already seen, this 
dictionary defines consciousness in terms of mind, and 
mind in terms of consciousness, so that nothing can be 
learned about consciousness in this dictionary. Conse- 
quently we have feehng defined in terms of what is, if any- 
thing, more unknown than itself. I am well aware that if 
we follow up the definitions of terms to the last stage of 
analysis, we are certain to run up against the unknown, for 
all our knowledge is relative and nothing is absolutely 
known. But it is well when defining a thing to do so if pos- 
sible in terms of what is more concrete and better known. 
Now in the case of feehngs I believe that we should begin 
with sensations and indicate that feelings are certain kinds 
of sensations or, at any rate, certain aspects of certain kinds of 
sensations. By doing so we should be defining feehng in 
terms of something that is more or less concrete and tan- 
gible and about which something is known. It may be that 
some will deny that feehngs have anything to do with 
sensations. But it seems to me that those who make such 
a contention would be denying the determination of psychic 
phenomena by physical forces. Certainly those who be- 
Heve in such physical determination of psychic phenomena 

1 The article on feeling in this dictionary is signed by J. M. Baldwin and G. F. 
Stout, who, as has already been noted, also wrote the articles on consciousness and 
mind in this dictionary. 



29S The Science of Human Behavior 

must believe that all psychic processes are initiated by 
physical stimuli, and these stimuli affect the nervous system 
by giving rise to sensations. So that sensations furnish 
the basis for feeHngs as we have seen they furnish the raw 
material for consciousness and as indeed they are the basis 
for all psychic phenomena. 

Some writers distinguish between feelings of pleasure and 
pain and feelings of pleasantness and unpleasantness on 
the ground that these latter feelings do not result directly, 
at any rate, if at all, from sensations caused by external 
stimuK. The theory held by some is that feelings of pleas- 
antness and unpleasantness are caused by changes in the 
intensity of the nervous current and not by stimulations 
received through specific sense organs.^ This theory is, 
therefore, similar to Spencer's theory that all painful and 
pleasurable feelings are due to changes in the intensity of 
the nervous current. It is, however, a mistake to assume, 
as is sometimes implied, that because feeUngs of pleasant- 
ness and unpleasantness are not due to external stimuli, 
they are not based upon sensations and that they are radi- 
cally different from painful and pleasurable feelings. In- 
ternal physiological processes may give rise to sensations 
just as well as external stimuh, so that if these pleasant 
and unpleasant feelings are due to the increase or decrease 
of the intensity of the nervous current they are quite as 
sensational in their origin as other feelings. Furthermore, 
as sensations with an affective aspect they cannot be radi- 
cally different from other painful and pleasurable feelings. 
As we have seen, all feelings are in all probability pleas- 

1 Cf. Max Meyer, The Nervous Correlate of Pleasantness and Unpleasantness, in 
the Psychological Review, Vol. XV, No. 5 (Sept. 1908). 



Consciousness 299 

urable or painful, and feelings of pleasantness and unpleas- 
antness differ from other feelings only in that they are 
more diffused and less localized than feelings which are 
due to sensations which are received through specific sense 
organs. 

Assuming, then, that feelings are certain kinds of sensa- 
tions, or, to say the least, certain aspects of certain kinds 
of sensations, it must be recognized that they play an im- 
portant part in the determination of behavior. As we have 
seen, painful feelings tend to inhibit the acts which give 
rise to them or to draw the animal away from the stimuli 
which cause them, while pleasurable feelings tend to re- 
enforce the acts which give rise to them and to draw the 
animal towards the stimuH which cause them. Feelings, 
then, are of importance, in the first place, as factors in 
the determination of behavior, and, in the second place, 
as forming a part of the contents of consciousness. Let 
us see what other psychic phenomena are included in the 
contents of consciousness. 

Emotions 

The emotions are usually regarded as important elements 
in consciousness. Later on I shall give reasons for think- 
ing that the emotions are feelings. But they have usually 
been discussed by themselves, apart from the feelings, and 
some writers seem to think that they are quite distinct from 
the feelings. For these reasons I shall discuss them by 
themselves at first and then discuss their relations to other 
feelings. 

There have been various theories in the past as to the 
nature of emotions. Some have thought that there are 



300 The Science of Human Behavior 

special organs for emotions which are stimulated to func- 
tion by external forces. But it is now pretty generally 
beUeved that the emotions accompany certain tendencies 
to action and are the by-products, so to speak, of these 
tendencies. This is the so-called James-Lange theory of 
the emotions, to which I have referred when discussing 
instinct. It is doubtful if a simple reflex action could be 
accompanied by an emotion, since the organic processes 
involved are not sufficiently complex. The instincts, there- 
fore, are these tendencies to action which are accompanied 
by emotions. As James has said, "an emotion is a tend- 
ency to feel, and an instinct is a tendency to act charac- 
teristically when in the presence of a certain object in the 
environment.'' 

The great question is as to how these tendencies to ac- 
tion give rise to emotions. Both James and Lange be- 
lieved, as we have seen, that emotions are the incidental 
results of the organic reaction. But James thinks that 
they result from the effect of the organic reaction on the vis- 
cera, while Lange thinks that they result from the effect 
of the organic reaction on the vasomotor or vascular system. 
Certainly the part played by the viscera in the emotions 
is quite evident, as illustrated in the heightened beat- 
ing of the heart in anger and other emotions, the contrac- 
tion of the blood vessels causing a blanching of the skin 
in fear and the expansion of the blood vessels causing their 
flushing in shame, the stimulation of the bowels in fear, 
etc. But it is likely that the vasomotor system also plays 
a part. An illustration of this may be the secretion of 
the lachrymal gland in grief. But there is not the space 
to discuss here the relative importance of the parts played 



Consciousness 301 

by the viscera and the vascular system in emotions. In 
the case of both the process which takes place must be 
somewhat as follows: We have seen that almost all the 
stimuli to action in animals with a nervous system come 
through this system. If action takes place, however, there 
is involved the cooperation of the muscles, viscera, vascu- 
lar system, etc. The movements of these parts of the or- 
ganism must react upon the nervous system to a certain 
extent, and the emotions appear to be some, if not, all of the 
results from this reaction. The reaction is principally 
upon the sympathetic system, which furnishes most of the 
nerves for the viscera and vasomotor systems. The emo- 
tions^ then, are the feelings which are aroused in the nervous 
system by these internal processes, and the movements of mus- 
cles, the viscera, etc., which accompany the emotions are their 
causes. 

It is true that emotions will sometimes arise when no 
external action takes place. One attempt to explain these 
cases was that of Darwin and Spencer, who thought that 
these were reminiscences of ancestral modes of behavior 
in response to certain stimuli where these modes of be- 
havior have in the main disappeared. But the theory as 
stated by these writers seemed to imply the transmission 
by heredity of acquired habits which, as we have seen, is 
very doubtful. It might happen that part of an instinctive 
tendency to a certain mode of action would die out as a 
result of changes in the nervous system, so that the organic 
reaction to the appropriate stimulus would be only sufficient 
to give rise to the emotion, but not to the external action. 
But it is more likely that these cases where an emotion is 
aroused without any external act taking place are due to 



302 The Science of Human Behavior 

some inhibitory force which checks the act, but not the 
emotion. Thus an acquired habit of self-control may 
restrain an individual from striking when the instinct of 
pugnacity is aroused, but cannot inhibit the rise of the emo- 
tion of anger which is accompanied by increased heart 
action, tense muscles, etc. Self-control may prevent an 
individual from fleeing from an object of danger, but can- 
not prevent the emotion of fear which is accompanied by a 
contraction of certain of the blood vessels, trembUng of 
the knees, etc. In fact, it sometimes happens that the emo- 
tion is strongest when the external act is inhibited, because 
action usually relieves the organic conditions which give 
rise to the emotion. This indicates how an emotion may re- 
enforce and strengthen a tendency to an action in order 
to secure the relief which comes through action. This is 
why emotions become powerful factors in the determina- 
tion of behavior. 

But certain experiments have been made which seem to 
contradict this theory that the emotions are aroused by 
the reaction of the viscera and other parts of the organism. 
Sherrington ^ has, by means of appropriate spinal and vagal 
transection in dogs, removed the sensation of the viscera 
and of all the skin and muscles behind the shoulder, and 
has destroyed the connection between the organs of con- 
sciousness and the whole of the circulatory apparatus of 
the body. Such animals have displayed the emotions of 
anger, joy, disgust, fear, etc., just as much as before the 
operation, thus seeming to indicate that these emotions 
can be aroused in the brain independently of the viscera, 
etc. Certain psychologists, such as Lloyd Morgan, ^ An- 

> The Integrative Action of the Nervous System, New Haven, 1906, pp. 255-268. 
' Animal Behaviour, 2d. edit., London, 1908, p. 92. 



Consciousness 303 

gell/ etc., have denied that these experiments have dis- 
proved the theory that emotions are caused by the reaction 
of the viscera and other parts of the body on the ground 
that the mechanism for these emotions had already been 
developed in these animals so that the emotions could be 
aroused independently of the viscera, etc. As Morgan 
puts it, *'the avenues of connection were closed after the 
motor and visceral effects had played their parts in the 
genesis of the emotion on the hypothesis that the emotion 
is thus generated. Although new presentative data of 
this type were thus excluded, their re-presentative after- 
effects in the situation were not excluded." Sherrington, 
however, has replied by stating that one of the dogs was 
but nine weeks old when the operation took place, and yet 
this animal displayed disgust when offered dog's flesh to 
eat. He thinks that it had not lived long enough for this 
emotion to be fixed in the brain so that it could be aroused 
independently of visceral stimulation. As he puts it, 
"disgust for dog's flesh could hardly arise from the experi- 
ence of nine weeks of puppyhood in the kennel." 

As a result of these experiments, Sherrington is inclined 
to believe that emotions originate in the brain and not in 
the viscera. He says: "We are forced back toward the 
likelihood that the visceral expression of emotion is second- 
ary to the cerebral action occurring with the psychical 
state. There is a strong bond of union between emotion 
and muscular action. Emotion * moves' us, hence the 
word itself. If developed in intensity, it impels toward 
vigorous movement. Every vigorous movement of the 
body, though its more obvious instrument be the skeletal 

1 Psychology, New York, igo8, p. 37i- 



304 The Science of Human Behavior 

musculature of the limbs and trunk, involves also the less 
noticeable cooperation of the viscera, especially of the 
circulatory and respiratory. The extra demand made 
upon the muscles that move the frame involves a height- 
ened action of the nutrient organs which supply to the 
muscles the material for their energy. This increased 
action of the viscera is colUgate with this activity of mus- 
cles. We should expect visceral action to occur along with 
the muscular expression of emotion. The close tie between 
visceral action and states of emotion need not therefore 
surprise us." 

Sherrington cites as further evidence of his theory the 
decerebration experiments of Goltz. Goltz kept ahve for 
many months a dog from whom the hemispheres of the 
brain had been removed. During all this time it gave 
no sign of fear, joy, affection, or sexual emotion, but it re- 
peatedly gave expression to anger and displeasure, both 
by gesture and by voice. This experiment seemed to 
indicate that a higher nervous organization is needed for 
the first set of emotions than is needed for anger and dis- 
pleasure. Sherrington thinks that these experiments fur- 
nish evidence "that emotion is primarily a cerebral reac- 
tion." But I do not think that this is necessarily the case, 
for the brain is just as necessary for emotion as a psychic 
phenomenon if the stimulus which gives rise to it comes 
from the viscera as it is if the emotion originates in the 
brain independent of the viscera. I do not suppose that 
any one who believes in the visceral or vascular origin of 
emotions thinks that these emotions are actually felt in 
these organs, but that,, on the contrary, all are agreed that 
all emotions are felt in the nervous system, and that as 



Consciousness 305 

psychic phenomena most, if not all, emotions manifest them- 
selves in the brain. 

It must now be evident, I think, that more experiments 
must be made before we can hope to know with certainty 
just where emotions originate. I believe, however, that 
we can say with certainty that the viscera and other inter- 
nal organs and the vasomotor system are involved in emo- 
tions as well as the nervous system. Sherrington expresses 
this opinion from his point of view in the following words : 
*'In view of these general considerations and of the above 
experiments, we may with James accept visceral and or- 
ganic sensations and the memories and associations of 
them as contributory to primitive emotions, but we must 
regard them as reenforcing rather than initiating the psycho- 
sis. Organic and vascular reaction, though not the actual 
excitant of emotion, strengthen it." 

I think that the preceding discussion of emotion must 
have shown that emotions arise out of sensations. The 
stimuH for these sensations may not come from outside, 
but they are none the less sensations. Many of them are 
kinaesthetic sensations which are caused by movements 
of the muscles. Moreover, they are sensations with a dis- 
tinctly affective aspect. That is to say, they are all of them 
sensations which are either pleasurable or painful and can 
be classified as such. // this be true, then the statement made 
earlier in this chapter that emotions are feelings has been 
sustained. They are, however, usually more powerful 
than ordinary feelings and accompany and reenforce cer- 
tain definite types of behavior, so that they play a larger 
part than ordinary feelings in the determination of behavior. 
Furthermore, they seem to impart an unusually rich ^'feel- 

X 



306 The Science of Human Behavior 

ing-tone," as some psychologists say, to consciousness. 
It is quite likely that they have a longer history than any 
other element in consciousness, since they are to a large 
extent contemporaneous with the instincts. If so, they 
form the earliest group of feehngs. I do not believe that 
they constitute consciousness when they stand alone, but 
when consciousness has made its appearance they add 
something to its character, as will be shown in the follow- 
ing chapter. 



CHAPTER XVI 

PERSONALITY, INTELLIGENCE, CONSCIOUSNESS, AND THE 
NATURE OF MIND 

Self-consciousness or personality based upon the integrated per- 
manent psychic elements, 307. — Self-consciousness as an idea, 309. — 
Multiple personality, 309. — The nature of voUtion, 311. — Subjec- 
tive and objective aspects of consciousness, 313. — The relation 
between consciousness and intelligence, 314. — The criterion of con- 
sciousness, 314. — The functions of consciousness, 315. — Conscious- 
ness as self-consciousness, 319. — Definition of consciousness, 321. 
Psycho-physical parallelism, 321. — Psycho-physical interactionism, 
322. — Definition of mind, 322. — Mind as including intelligence and 
consciousness, 322. — Mental processes determined by minute physio- 
logical processes, 322. — Mind as a stage in the determination of 
certain kinds of behavior, 323. — The relation between mind and 
matter, 323. — The criterion of mind, 324. — Is our knowledge of 
mind subjective or objective, 325. 

The highest plane of consciousness is reached in self-con- 
sciousness or the sense of personality. Self-consciousness, 
like consciousness, is frequently spoken of as a distinct 
entity. But it is no more an entity than conscious- 
ness. In fact it is a less concrete and more intangible 
thing than the sensations, feelings, and emotions which 
have been discussed. We can best understand its nature 
by considering briefly the conditions under which it appears. 

Self-Consciousness 

Self -consciousness is based upon the more or less permanent 
psychic elements. That is to say, it is essential for the ap- 

307 



308 The Science of Human Behavior 

pearance of self-consciousness that there should be a cer- 
tain number of sensations, feelings, and ideas which are 
more or less permanent. It is hardly conceivable that self- 
consciousness could appear in an individual whose feelings 
and ideas were constantly changing so that his psychic 
equipment would become entirely different within a short 
interval of time. Assuming, then, such a more or less per- 
manent equipment of psychic elements, self-consciousness 
appears as a result of the process of integration which gives 
to these diverse psychic elements a certain unity. This inte- 
gration takes place by means of the same mechanism which 
performs the other types of integration which have been 
discussed, namely, the central nervous system and in partic- 
ular the association areas of the brain. The kind of in- 
tegration involved in personaUty is, however, different from 
that involved in instinct, for example, in that it is not in- 
herited but is acquired in the course of the Hfetime of the 
individual. This is to be expected of any kind of integration 
which grows in large part out of the association areas for, 
as we have seen, these areas are not specialized at birth but 
become so during the life of the individual. For the same 
reason consciousness in general is in large part if not entirely 
an acquired character, for it also grows in large part out of 
these association areas. 

It is, of course, impossible to tell just when the sense of 
personality first made its appearance, but it has probably 
existed in a very rudimentary form in many of the higher 
animals. This rudimentary form is probably in the main 
a state of feeling. It arises out of the harmonious and more 
or less permanent relations with each other of certain feel- 
ings and images. Hobhouse has made a good attempt to 



Personality, Intelligence, Consciousness 309 

describe it when he says that a dog or ape has "a self, i,e. 
a pervading identity and permanent character, is aware 
at least of its present needs and seeks to identify them. 
What we miss is evidence that the self is present to it as a 
persistent identity in such a way, for example, as to shape 
the choice of immediate ends by considerations of lifelong 
welfare. The self of which the animal is conscious is a 
"very small fragment as compared with the self of which 
the man is aware." ^ 

But self-consciousness cannot develop very far until it 
becomes an idea, and its evolution as an idea has been prin- 
cipally if not entirely among men. To trace fully the de- 
velopment of the idea of personality would be to trace 
the whole course of human, mental, and social evolution. 
It is doubtful if the idea of personaHty could be conceived 
by an individual Hving in isolation. This idea grows out 
of the observation of the likenesses and differences between 
the observer and other individuals, so that it is in large 
part a social product. The development of language played 
an important part, for it gave to the idea of personality 
definiteness and clearness just as it has done so to all ideas. 
Unfortunately I have not the space to discuss this subject 
at greater length, but these few suggestions give a sHght 
indication of the causes for the superior development of 
human self -consciousness. 

That self-consciousness is not a distinct entity is indi- 
cated by a number of the phenomena which characterize 
it. For example, the phenomenon of so-called multiple 
personaHty is such an indication. Every personaHty is 
to a certain extent multiple. That is to say, each individual 

* Mind in Evolution, London, igoi, p. 312. 



310 The Science of Human Behavior 

possesses several different sets of feelings and ideas, each of 
which is stimulated by an appropriate environment or by 
suitable physiological conditions. But ordinarily these 
sets are not separated from each other so greatly but that 
the individual recognizes that they belong to the same 
personaHty. Under pathological conditions, however, the 
separation between these different sets may become so 
great that the individual does not recognize them as be- 
longing to the same personality, so that there arise the 
phenomena of multiple personaHty and of mental alienation. 
Hobhouse indicates the varying degrees in which personality 
is multiple in the following words : *'In a sense, it is scien- 
tifically true that the business man, who has spent the day 
in besting a rival, is not the same person as the father who 
comes home to romp with his children. The outward and 
visible semblance is the same, but within it there are two 
quite different masses of thought, emotion, and will, each 
forming an interconnected system by itself, yet standing 
in no logical or moral relation with the other. When the 
cleavage becomes extreme, we speak of 'double personality, ' 
of alienation, or insanity. But the germ of this sort of 
madness is in all of us." ^ 

The effect of drugs and narcotics in disintegrating the 
consciousness of self temporarily and sometimes perma- 
nently is a significant indication that it is not a distinct and 
permanent entity. The way in which the sense of personal 
identity is lessened and sometimes changed in dreams is 
further indication of this fact. These phenomena cannot 
be explained on the ground of a subconscious self.^ To 

* op. cit., p. 302. 

* Cf. A. H. Pierce, An Appeal from the Prevailing Doctrine of a Detached Sub- 
consciousness, in Studies in Philosophy and Psychology Dedicated to C. E. GarmaHt 
Boston, 1906. 



Personality, Intelligence, Consciousness 311 

do so would be to assume the existence of two distinct, 
permanent entities, whereas we have seen that we have no 
reason to beUeve in the existence of even one such entity. 
These phenomena can be explained only on the ground of 
a unification of the contents of consciousness by the higher 
integrative mechanism of the central nervous system, which 
unification can, however, be destroyed in varying degrees 
or can be disintegrated into several smaller unities. 

Volition 

The will or volition is usually regarded as an expression 
of the self. There is not the space to enter upon an extended 
discussion of the many theories of the will which have been 
proposed, but I hardly need to say that science does not 
accept any theological or metaphysical doctrine of a will 
which is a distinct entity and which is independent of 
natural forces. No more can science accept a theory of 
will which regards it as immanent in the universe. So far 
as anything like will or volition exists at all it is a charac- 
teristic of consciousness and probably should be limited 
to self-consciousness. Volition manifests itself when the 
idea of an act, which has grown out of memory images of the 
act, and other contents of the memory influence behavior. 
Thus a stimulus to a certain action may be received, and 
the act will be performed unless the contents of the memory 
consciously inhibit it, in which case the volition will have 
been exercised. If the inhibition is unconscious as the re- 
sult of habit, it cannot be regarded as voHtional. Or the 
idea of a certain act may be aroused and serve as a stimulus 
to its performance, in which case a voHtional act will have 
been performed. In each case of a volitional act the stimuli 



312 The Science of Human Behavior 

to action are either inhibited or reenforced by the contents 
of the memory and other characteristics of the individual, 
and the process is accompanied by consciousness, so that 
there frequently arises the illusion that the act is determined 
by the self, independent of external forces. Hobhouse has 
described the will very well in the following words: **The 
will is not to be regarded as an additional impulse, or as a 
force existing outside impulses and operating upon them. 
It is rather the system or synthesis of impulses, the broad 
practical bent and tendency of one's nature. Now here 
as elsewhere the development as we pass from a lower to 
a higher stage consists primarily in a growing explicitness. 
It is quite possible that even in animal Ufe, when there is a 
conflict of desires, that one tends to prevail which is most 
intimately bound up with the animal's whole mode of Hfe. . . . 
The new development is merely that those broad tendencies 
of the character which before operated, if at all, obscurely 
and unconsciously, have now a definite conception to guide 
them. The nature of the self, its character, its duties, the 
wider life of which it is a part, now become conceptions, 
ideals, or principles, which appeal to the personality as a 
whole, just as particular satisfactions appeal to special 
impulses. Just as the special impulse when it formulates 
its end into an idea becomes Desire, so what we have called 
the broad impulses of the personality, when their end is 
defined by conception, constitute Will." ^ 

Nature of Consciousness 

The preceding has been a brief discussion of the contents 
of self -consciousness. The description of these contents 
» op. cit., p. 313- 



Personality, Intelligence, Consciousness 313 

has, I fear, sometimes been rather vague. But such vague- 
ness is to a certain extent inevitable in connection with such 
intangible phenomena, and the same is even more true with 
respect to consciousness in general. I shall, however, 
endeavor now to set forth as definite a theory of the nature 
of consciousness as is possible with the known facts. 

Many psychologists have asserted that consciousness 
is purely subjective, and a psychological definition of con- 
sciousness which made no attempt to define it in objective 
terms has been quoted. One psychologist specifically 
states that "consciousness we can only define in terms of 
itself." ^ Two questions may be raised in connection with 
this position. In the first place, does anything purely sub- 
jective exist? That is to say, does anything subjective, 
such as an idea or a feeling, exist entirely independent of an 
objective basis, such as a nervous system ? It if does, we 
must accept a duahstic philosophy which, as we have seen, 
is hardly compatible with the standpoint of science which is 
trying to reduce all phenomena to the same terms. It 
seems, then, as if the subjective should be regarded as one 
aspect of the objective or as the objective looked at from a 
certain point of view. In the second place, if consciousness 
is purely subjective, can it be studied by science ? It seems 
quite clear that tangible phenomena are necessary for any 
scientific study, so that if consciousness presents no such 
phenomena it is useless to attempt a scientific study of it. 
However, for the reasons given above, we are justified in 
beheving that consciousness is objective if it exists at all, 
and that consequently it is possible to study it scientifically. 

What, then, is consciousness as an objective phenomenon, if 

» Angell, op. cit., p. i. 



314 The Science of Human Behavior 

it exists at all? I have already suggested that it may be a 
form of behavior. If so it must be a form of movement and 
must involve the expenditure of energy.^ It cannot be an 
inherited form of behavior, but must be a variation from 
such behavior. I have already raised the question as to 
whether consciousness is identical with intelligence, which 
is a form of varied behavior. I have quoted Loeb's con- 
ception of consciousness as the activity of the associative 
memory which, according to him, is identical with intelli- 
gence. I have also quoted Herrick's, which also seems to 
identify the two. But I think the preceding discussion 
must have shown that the two are not identical. Con- 
sciousness cannot develop very far without the ideas which 
intelligence furnishes it and which constitute an important 
part of its contents. But consciousness includes the feel- 
ings as well, and it may be that consciousness originated 
in the form of feeHng. This may be putting its origin too 
far back, and it may be that it did not appear until after 
the beginning of intelUgence. It may even be best not to 
recognize consciousness until the idea of the self has made 
its appearance. But at whichever point we place the origin 
of consciousness it is evident that it contains something 
more than the ideas which belong to intelligence, so that 
the two are not entirely identical. 

Some writers have regarded the ability to learn as the 
criterion of consciousness.^ It is evident that this would 
depend upon the answer to the question as to when con- 
sciousness originated which I have just discussed. If con- 

' Cf. W. p. Montague, Consciousness as Energy, in Essays in Honor of William 
James, New York, 1908. 

' Cf. Mary W. Calkins, The Limits of Genetic and of Comparative Psychology, in 
the British Journal of Psychology, Vol. I, Pt. 3 (Jan. 1905). 



Personality, Intelligence, Consciousness 315 

sciousness appeared before intelligence, then the ability to 
learn would not always be a test of consciousness. If the 
two appeared at the same time, it would always serve as a 
test. If consciousness appeared after intelligence, a very 
slight abiHty to learn would not necessarily indicate the 
presence of consciousness. However, in most cases and 
for all practical purposes the ability to learn serves very 
well as a criterion of consciousness for, as we have seen, 
intelligence and consciousness accompany each other all 
the time, with the possible exception of the earhest stages 
of the one or the other. The same is true of varied behavior 
as a criterion of consciousness. 

Let us see just how consciousness operates and how it 
influences behavior. It goes without saying that this is 
the principal reason for our interest in consciousness, and 
for that matter it is the principal reason for studying it, 
for if it did not influence behavior, it would be a waste of 
time to study it. Consciousness is of importance only as 
what Lloyd Morgan calls "effective consciousness," which 
is "that which enables an animal to guide its actions in the 
light of previous experience." ^ 

As we saw in the last chapter, Romanes, Spencer, and 
others beHeved that consciousness appears between stimu- 
lus and response. Herrick displays the same idea when he 
says that it makes its appearance between anticipation 
and consummation. "In the storm and stress of this 
interval just preceding the consummatory reaction the 
higher mental faculties are born." ^ Now by this is not 
meant, of course, that during this interval a spirit or fairy 

1 Habit and Instinct, London, 1896, p. 127. 

2 The Evolution of Intelligence and its Organs, in Science, Vol. XXXI, No. 784 
(Jan. 7, 1910), p. 13. 



316 The Science of Human Behavior 

appears which influences the response to the stimulus. 
But during this interval ideas and feelings may be stimu- 
lated and may influence the response and therefore the 
behavior which results from the stimulus. It is evident 
that in order to permit consciousness to appear such an 
interval must exist, and that the pathway from stimulus to 
response must not be so firmly fixed that nothing can 
change it. As Royce says, consciousness "attends those 
processes which, while involving the cortex, are of a decid- 
edly complex grade and of a relatively hesitant character, 
or which come in consequence of the graver interferences 
on the part of our environment." ^ It is evident that these 
conditions can be found only in animals with a nervous 
system which is relatively highly developed and possesses 
the higher nerve centers. So that, as Meyer says, "con- 
sciousness accompanies processes in the ' higher ' connecting 
neurons, the higher 'nerve centers,' whereas processes 
restricted to the lower centers may go on without any con- 
sciousness." ^ It is therefore a serious mistake when Clap- 
arede, who is a psycho-physical parallelist, says that "the 
question of the greater or less intelligence of animals no 
more prejudges that of their degree of consciousness than 
a concept of a tropism implies the absence of consciousness. 
These are two questions the solutions of which neither 
prejudge nor mutually exclude each other. We ought to 
oppose the simple to the complex, not the simple to the 
conscious^ ^ On the contrary, the degree of consciousness 
does correspond directly to the degree of complexity of the 
neural mechanism. 

But even in complex nervous systems there are a great 

> Outlines of Psychology, New York, 1904, p. 81. ' Op. cit., p. 306. 

» Op. cit., p. 314. 



Personality, Intelligence, Consciousness 317 

many responses which are unconscious because the pathway 
from stimulus to response is firmly fixed so that there is no 
chance for variation. In fact it is very doubtful if even 
in man the number of conscious actions ever exceeds the 
number of unconscious ones. In the first place, there are 
the inherited modes of reaction which never become varied 
in the course of individual experience. This is especially 
true of the reactions controlled by the lower nerve centers. 
In the second place, there are the large number of acts 
which were at first conscious because they involved individ- 
ual adjustment to the environment, but which have become 
habitual, that is to say, the pathway has become so firmly 
fixed that there is little chance of variation taking place, 
so that the acts are unconscious. It is this transition from 
conscious to unconscious behavior which has led certain 
writers to think that all behavior was at first conscious, but 
I have already pointed out the fallaciousness of this idea. 
It appears then as if consciousness acts in accordance with 
the law of parsimony. It appears when needed but dis- 
appears as soon as that need ceases. As Herrick has said : 
*'Here we see how intelKgence and feeling are developed 
as the servants of action. They do not appear so long as 
the action can be effected without them, and they vanish 
as soon as the reflex machinery of an adaptive action is 
set in motion." ^ 

Various attempts have been made to state just how con- 
sciousness influences behavior. For example, Minot says 
that "the function of consciousness is to dislocate in time 
the reactions from sensations." ^ He apparently means 

^ op. cit., p. 1 6. 

* C. S. Minot, The Problem of Consciousness in its Biological Aspects, in Science, 
Vol. XVI, No. 392 Quly 4, 1902). 



318 The Science of Human Behavior 

that it can delay the reactions to certain sensations. Later 
on he asserts that ^^consciousness has the power to change tJie 
form of energy y and is neither a form of energy nor a state of 
protoplasm,^ and that *'the universe consists of force and 
consciousness." Apparently, therefore, he regards con- 
sciousness as a sort of mystical force quite distinct from 
natural phenomena. This conception is, as we have seen, 
quite fallacious. But his description of what is done by con- 
sciousness is more or less accurate so far as it goes, though 
this function is performed not by a mystical force but by 
the higher centers of the nervous system. It is, however, 
true, as has been pointed out by a number of critics, that 
this function may be performed by an unconscious mecha- 
nism. For example, an alarm clock is so constructed that 
it will delay for many hours the reaction to the stimulus 
of being wound up. So that this description of the func- 
tion of consciousness is not quite adequate. 

A more adequate statement of the function of conscious- 
ness has been made by Judd.^ He thinks that inner self- 
sufficiency and increasing autonomy of the individual, 
making it more and more independent of the environment, 
form the end toward which organic evolution is progressing. 
Consciousness plays a more and more important part in 
this process, and consequently he defines it as follows : 
''Consciousness is a function which promotes self-sufficiency 
by literally taking up the environment into the individual 
and there remoulding the absorbed environment in conform- 
ity to individual needs." He believes that it has become the 
principal factor in the Hfe of man, going so far as to say 

* C. H. Judd, Evolution and Consciousness, in the Psychological Review, Vol, 
XVII, No. 2 (March, 1910). 



Personality, Intelligence, Consciousness 319 

that "consciousness is the essential fact in human life as I 
have attempted to show. What man does with his en- 
vironment depends upon consciousness." It has, however, 
been the intellectual rather than the affective part of con- 
sciousness which has played the principal part. "Human 
behavior is not aimed at maintaining oneself within the en- 
vironment, it is aimed rather at complete remoulding of the 
whole environment, and the chief instrument in this process 
of remoulding is intellectual comparison and deHberation, not 
emotion." Judd tends to regard consciousness too much as 
if it is an entity. For example, he says that "consciousness 
is a cause of events in the physical world." We have seen 
that we have no tangible evidence of such a thing as con- 
sciousness, and it is at most a name for certain relationships, 
or for a certain process. But in his discussion he gives a 
fairly good description of this process. 

Consciousness, then, exists whenever behavior is influenced 
by ideas or by feelings. It is true that this statement still 
leaves the conception of consciousness rather vague. Our 
conception of it could be made more precise by limiting 
consciousness to self -consciousness, and there are a number 
of reasons why it would be well to do so. While it is im- 
possible to determine just when the sense of personality 
first made its appearance, we can probably come nearer to 
it than we can to determining when consciousness in gen- 
eral first made its appearance. Furthermore, the sense 
of personality marks off a stage in mental evolution more 
definitely than does consciousness in general. A few psy- 
chologists have identified consciousness with self-conscious- 
ness. For example. Miss Calkins says: "Animals, if 
they are conscious at all, must be conscious of selves, for 



320 The Science of Human Behavior 

consciousness of any other sort is inconceivable. To be 
conscious simply means to be conscious of oneself in this 
or that or the other situation." ^ She goes on to explain 
that she does not mean the "definite, discriminated, re- 
flective self-consciousness of the psychologist or philos- 
opher," but a vague sense of personaHty possessed by 
young children and by some of the animals besides man. 
Royce also seems to have this idea when he says that "a 
state of consciousness exists when somebody is conscious 
of that state. When nobody is conscious of that state, 
it does not exist." ^ It may be that these writers think 
that the sense of personality originated as early as feelings 
and ideas, in which case their identifying consciousness with 
it does not make consciousness any more precise in meaning.^ 
If, however, they think it appeared later, to identify con- 
sciousness with it is to make the meaning of consciousness 
more precise. 

Other psychologists have opposed the limitation of the 
term consciousness to the sense of personality. Thus Ward, 
who identifies consciousness with experience, says of con- 
sciousness that "it is continually confused with self-con- 
sciousness, which was its original meaning; and thereby 
the errors of intellectualism, which we have just discussed, 
are apt to be perpetuated and a part of experience mistaken 
for the whole." ^ It seems quite evident that he has in 
mind a well-developed idea of the self, while Miss Calkins 

» op. cit., p. 284. « op. cit., p. 108. 

* Miss Calkins may mean to imply this when she says that all consciousness in- 
volves "an experience qualitatively similar to that later consciousness which every 
one agrees to call self-consciousness." {A Reconciliation between Structural and 
Functional Psychology, in the Psych. Rev., Vol. XIII, No. 2 [March 1Q06]). 

* James Ward, On the Definition of Psychology, in the British Journal 0/ Psychol- 
ogy, Vol. I, No. I Gan. 1904). 



Personality, Intelligence, Consciousness 321 

and Royce have in mind a much more elementary form of 
self -consciou sness. 

It goes without saying that the meaning of words is 
determined by usage, and it is true to-day and probably 
will remain so for some time that consciousness has the 
wider and therefore vaguer meaning, even though it would 
be preferable for the reasons suggested above to Hmit it 
to the sense of personaHty. I have not the space to discuss 
the conception of consciousness further, but hope that the 
preceding discussion gives some indication how conscious- 
ness influences behavior. I can only repeat that conscious- 
ness is a complex process made up of feelings and ideas which 
are unified by the sense of personality which may begin as a 
vague feeling J but which becomes in course of time a clear-cut 

idea. 

Nature of Mind 

We have now discussed the nature of intelligence and of 
consciousness and are prepared to take up the subject of 
the nature of mind. There have been many theories as to 
the nature of mind, so that it would be impossible to discuss 
all of them here. I will speak of two of them which have 
been widely held in the past and which are still held by 
many. The first is the theory of psycho-physical parallel- 
ism. This theory, in the words of one of its adherents, 
"regards the processes of the material universe (including 
those of the physical organism) as a closed chain of cause 
and effect, which is altogether removed from any psychical 
influence. Mental process is a concomitant of certain 
highly complex material processes, but not anything that 
affects these processes themselves." ^ That is to say, ap- 

1 E. B. Titchener, Were the Earliest Organic Movements Conscioiis or Unconscious ^ 
in the Pop. Sci. Mo., Vol. LX, p. 458 (March, 1902). 

y 



322 The Science of Human Behavior 

parently, according to this theory, mind is something super- 
phenomenal, if not supernatural, which for some unaccount- 
able reason always accompanies certain material processes 
without, however, affecting these processes. The second 
theory regards mind as capable of causal interaction with 
body.^ That is to say, it assumes, like the parallelist theory, 
that mind accompanies certain bodily processes, but differs 
from it in assuming that mind influences these bodily pro- 
cesses and is influenced by them. It is evident that both of 
these theories regard mind as being a distinct entity of a 
superphenomenal if not supernatural sort. It must also 
be evident that science cannot recognize anything of this 
sort of which it can have no tangible evidence. To assume 
the existence of such an entity cannot be called a scientific 
theory, but the most speculative sort of an hypothesis. 

What, then, is mind ? It is quite likely that we should 
be better off if the word could be abolished from the lit- 
erature of the sciences which study the attributes of ani- 
mals because of the difhculty of assigning to it a definite 
meaning. But since the term is now firmly intrenched in 
general use, it is incumbent upon one who is trying to de- 
scribe the factors which determine behavior to Umit its 
scope and meaning as precisely as possible. 

It seems to me that mind is simply a general nam^ for the 
phenomena which we have been studying under the heads of 
intelligence and consciousness. If this is correct, then it is 
evident that mental processes are determined by minute and 
refined physiological processes which take place in certain 
parts of the central nervous system. We may then speak of 

* For an elaborate defense of psycho-physical interactionism, see William Mc- 
Dougall, Body and Mind, A History and a Defense of Animism, New York, 191 1. 



Personality, Intelligence, Consciousness 323 

mind as a stage in the determination of certain kinds of he- 
havior. It is the stage between the reception of the stimulus 
through a sense organ or otherwise and the discharge of an 
impulse to a motor organ which causes an external form of 
behavior. This stage manifests itself to the person experienc- 
ing it in the form of images, ideas, feelings, emotions, etc., 
while its presence is made known to the observer by means of 
certain kinds of variations in behavior. As we have seen, 
this stage may have great influence upon the behavior 
which is to result, so as to change completely the character 
of this behavior. 

I believe that the preceding discussion explains satisfac- 
torily the so-called "power of mind over matter'' and the 
alleged superiority of mind over matter whicii are fre- 
quently regarded as very mysterious characteristics of 
mind. It is the quantitative disproportion between the 
apparent cause and the apparent result in these cases of 
"the power of mind over matter" which has led to the be- 
lief that mind is immensely superior in quahty to matter 
and entirely different from it. It is therefore beUeved that 
a causo-mechanical explanation of mental and social phe- 
nomena is impossible. But the preceding discussion has 
shown that there is nothing mysterious about this power, 
but that similar phenomena take place constantly in nature 
whenever a small amount of molecular or molar force re- 
leases a large amount of molecular or molar force. We 
see this whenever a small amount of force in the form of 
heat is appHed to a combustible such as dynamite and results 
in the dissipation of a large amount of force. It has even 
been suggested that a process of radio-active change started 
in the elements might result in the disintegration of the 



324 The Science of Human Behavior 

earth. ''Professor Rutherford has playfully suggested 
to the writer the disquieting idea that, could a proper 
detonator be discovered, an explosive wave of atomic dis- 
integration might be started through all matter which would 
transmute the whole mass of the globe and leave but a 
wrack of heHum behind." ^ 

The mind, therefore, works like the trigger of a gun or a 
^ button which releases an electric current which explodes 
a mass of nitroglycerin. The amount of energy involved 
in the mental process is entirely disproportionate to the 
amount involved in the behavior which it influences and 
may even control. But this does not prove that it is ab- 
solutely different qualitatively from other material pro- 
cesses. 

Various attempts have been made to devise a criterion 
which will indicate whether or not mind is present. For 
example, Royce ^ enumerates as the ''physical signs of the 
presence of mind" discriminating sensitiveness, docility, by 
which he means the capacity shown by an animal in its 
acts "/o adjust these acts not merely to a present situation, but 
to the relation between this present situation and what has 
occurred in the former life of this organism,^ ^ and mental 
initiative. Yerkes ^ has improved upon Royce by recog- 
nizing structural criteria as well. He enumerates as struc- 
tural criteria of mind organization, neural-organization, and 
neural-specialization, and as functional criteria discrimina- 
tion, docility, and initiative. I think, however, that this 
chapter has shown that there can be no criterion or criteria 
of mind apart from the criteria of intelligence and conscious- 

» W. C. D. Whetham, The Recent Development of Physical Science, Philadelpbiia, 
1904, p. 343. « Op. cit., chap. II. » Op. cit. 



Personality, Intelligence, Consciousness 325 

ness which I have described, and reference to these criteria 
will show that they include all that Royce and Yerkes in- 
clude in their criteria of mind. 

I have now completed this discussion of intelligence and 
consciousness and of the nature of mind in general. It 
may seem that the conception of mind presented is very 
vague, but I think that it must be evident by this time that 
the phenomena grouped under this term are very diverse. 

Before closing this chapter I wish to discuss briefly the 
question as to whether our knowledge of mind is purely 
subjective or partly objective. Many psychologists be- 
lieve that it is purely subjective, thus placing psychology 
upon an entirely introspective basis. Looked at from one 
point of view, this may seem to be true. It is true that 
sensations, ideas, feehngs, etc., as such, are experienced 
only by the subject. But the behavior which results from 
them may be observed by another, and, as we have seen, 
the character of these psychic phenomena has to be de- 
scribed in large part in terms of behavior. Furthermore, 
scientific research has shown that these phenomena are 
determined by neural processes which may be observed. 
The aspects which psychic phenomena manifest to the 
subject, on the one hand, and to the outside observer, on 
the other hand, have been described by Montague in the 
following words: "What I, from within, would call my 
sensations are neither more nor less than what you, from 
without, would describe as the forms of potential energy 
to which the kinetic energies of neural stimuli would nec- 
essarily give rise in passing through my brain." ^ The fact 

* William P. Montague, Consciousness as Energy, in Essays in Philosophy and 
Psychology in Honor of William James, New York, 1908. 



326 The Science of Human Behavior 

that some observers have been able to introspect their 
mental processes more effectively because of their knowl- 
edge of these neural processes indicates that there is an 
objective as well as a subjective source of knowledge re- 
garding mind. To deny the possibility of such objective 
knowledge is, as has been pointed out by several writers, 
to deny the possibility of a comparative psychology, and 
we have seen how important this branch of psychology is 
for the reconstruction of mental and social evolution. 



CHAPTER XVII 

THE BEGINNINGS OF SOCIAL EVOLUTION 

Definitions of association and society, 327. — Colonial species, 
328. — Is there an inborn associative tendency? 329. — The ex- 
ternal, environmental forces for association, 330. — The degree of 
correlation between organic and social evolution, 331. — Internal 
forces for association, 334. — Inborn and acquired characteristics, 
335. 

So far I have been discussing the behavior of living beings 
in the main as if they were isolated from each other. But 
the great majority of animals live intermittently or per- 
manently in association with other animals, and their be- 
havior is more or less affected by such association. So 
that in any comprehensive survey of the forces that deter- 
mine behavior it is necessary to discuss association. In 
the following chapters I shall describe the fundamental 
types of association and the earlier forms of association 
among men, making some attempt to explain their causes. 

In the discussion of this subject, as in the discussion 
of so many others, questions of terminology immediately 
arise. What do we mean by such words as association 
and society ? By association might be meant simply that 
certain animals are in close proximity to each other. But 
this would not necessarily involve their affecting each 
other's behavior so that such association would be of no 
significance for the determination of behavior. By as- 
sociation is therefore meant usually, the sort of proximity which 

327 



328 The Science of Human Behavior 

results in affecting behavior. But the meaning of the term 
is frequently Hmited still further so as to apply only to 
proximity which affects behavior through mental interaction. 
By a society is usually meant a group characterized by more 
or less permanent association. I shall not attempt to define 
more specifically the technical meanings of these terms at 
this point, but will turn to the discussion of the ways in 
which animals come into proximity with each other and the 
effect which such proximity has upon their behavior. 

We have seen that the living cell is the unit in the organic 
world. Among the protozoa a single cell forms an organ- 
ism. Metazoan animals are formed of aggregations of 
cells. Such aggregations are sometimes called associations. 
Some protozoan species and some of the lower metazoan 
species form colonies in which the individual members are 
organically connected with each other. ^ These connections 
exist as aids to nutrition. In some of the colonial species, 
as, for example, the infusoria which form colonies, there 
is no vascular connection. In other colonial species, as, 
for example, some of the polyps, mollusks, worms, etc., 
there is vascular connection which increases considerably 
the degree of interdependence in the nutritive processes. 
A certain degree of physiological division of labor develops 
in some of these colonial species. In fact, in some of these 
species the relations between the individual members be- 
come so close as almost to make each colony a distinct 
organism. These colonies also are sometimes spoken of as 
associations, and even as societies. It is evident, however, 
that if we are to accept the definitions of association and of 

* E. Perrier, Colonies Animales, Paris ; A. Espinas, Des Sociitis Animoles, Paris, 
1878. 



The Beginnings of Social Evolution 329 

society which have been suggested, these aggregations can- 
not be regarded as associations or societies, even though a 
high degree of interdependence may exist among them, be- 
cause there is no mental interaction. Nevertheless, the 
study of these aggregations is of importance for social 
evolution, for it may be that this inborn tendency to unite 
persists throughout the rest of organic evolution and fur- 
nishes the occasion for the mental interaction which de- 
velops later. 

As yet we know nothing definite about such an inborn associative 
tendency. Petrucci suggests some of the small amount of evidence 
which we have with regard to it and some of the possibilities in the 
following passage : "When we reach the precursors of the vertebrates, 
the prochordates, we find colonial fife, and in the habits of the am- 
phioxus ^ which joins together several individuals to swim in ribbons 
there still expresses itself an affirmation of colonial life, a grouping 
of individuals. Can we go back still further beyond this remote 
form and claim to find an origin? Then we come to the very con- 
stitution of metazoan organisms, to the series of constitutive stages 
which, by successive differentiations and integrations, have reaHzed 
the type of the superior organisms upon the basis of associations or 
colonies of unicellular individuals originally alike. In his work on 
animal colonies, Edmond Perrier connects with this type of structure 
the four branches of the ringed worms, the mollusks, the articulates, 
and the vertebrates. Since the researches of Durand de Gros, it is 
known how this polyzoic constitution of beings has remained engraved 
upon their nervous system; it is possible to attach the associative 
tendency, manifested in so general a way in the animal world as a 
whole, to these primitive constitutions which have written them- 
selves upon the very structure of the individual and which are pro- 
jected as psychic acts into its external activity." ^ M. Petrucci goes 
on to express the opinion that in this "associative tendency" we have 
a manifestation of a universal rhythmic movement which manifests 

1 A low form of vertebrate. 

* R. Petrucci, Origins polyphyUtique, homotypie et non-comparabiliti directe des 
sociiies animates, Brussels, 1906, pp. 1 21-12 2. 



330 The Science of Human Behavior 

itself also in chemical affinities and in the force of gravity, so that 
" the associative tendency becomes a peculiar expression of this enor- 
mous rhythm which measures the evolution of the universe and which 
engraves itself, under a peculiar aspect, in the irresistible impulse 
by which the animal world is guided." 

But it is best for the present to treat very critically any 
such theory of an associative tendency, for there is very 
little evidence of its existence as yet. In the light of the 
preceding chapters it must be evident that it must be re- 
duced to the concrete terms of specific forces before we can 
be sure of its existence. In other words, it must be shown 
to exist in the form of tropic reactions in the lower animals 
and of reflexes in the animals with a nervous system. 
Simply because these animals come together, it does not 
necessarily follow that it is due to an associative tendency. 
Certain external forces bring them together. For example, 
animals living in the water will gravitate towards the area 
where the temperature is most favorable for their life pro- 
cesses. If this area happens to be small, a large number of 
the same species may be found in close proximity to each 
other, and yet have come together quite independently of 
each other. The pressure of the water may also influence 
this orientation. Thus it is that large shoals of fish are to 
be found in certain strata of water which is to be explained 
in part at any rate by the temperature and the pressure. 
Furthermore, the location of food determines the orienta- 
tion of the members of all species to a large extent. If the 
food of a species is distributed over a small area, the members 
of the species will be forced to come together in the course 
of their food quest. 

But the members of a species may influence each other 



The Beginnings of Social Evolution 331 

to come together without any associative tendency being in 
existence. For example, in discussing the behavior of the 
lower animals I have mentioned such a case in connection 
with certain unicellular animals which excrete a certain 
chemical. If a number of members of one of these species 
come into close proximity to each other by accident, the 
water in that region becomes more or less fully charged with 
this chemical. If, then, these animals react negatively 
when they strike the boundaries of this chemicated area in 
the manner described earlier, they will be held in this area 
in close proximity to each other. Other animals coming 
into the same area will be held in similar fashion, so that 
in course of time there may be a large aggregation due to 
the physiological processes of these animals. But this 
could hardly be regarded as a manifestation of an associa- 
tive tendency on the part of these species. 

It goes without saying that social phenomena are a part 
of universal phenomena and that social evolution is a part 
of the general evolutionary process. But in trying to 
explain these phenomena it does not help much to postu- 
late an associative tendency the nature of which we are 
unable to explain. The same is true of the so-called gre- 
garious instinct which is frequently cited in attempting 
to explain the later stages of social evolution and which we 
shall discuss later. Therefore, without assuming that an as- 
sociative tendency has necessarily been at work through- 
out organic evolution, for some would extend this tend- 
ency to the vegetable as well as to the animal world, let us 
discuss briefly the probable causes for social evolution. 

The phenomena of association have displayed themselves 
at many points in organic evolution and among many 



332 The Science of Human Behavior 

species. Is it possible to arrange these phenomena in their 
evolutionary order so that each group will have evolved 
directly from the group which precedes it? I think it is 
evident that this can be so for social phenomena no more 
than it is for organic phenomena. There have been many 
divergent Hnes of social evolution just as there have been 
many divergent Hnes of organic evolution. Along some of 
these divergent lines social evolution has proceeded very 
far, quite independent of other Hnes of evolution. So far 
as social evolution has been due to hereditary causes, the 
divergence must always have been quite as great as the 
divergence in the organic series. So far as social evolution 
has been due to other than hereditary forces, the degree of 
divergence has depended upon conditions which will be 
discussed later. This does not mean, however, that each 
divergent line if traced back far enough does not come to a 
common source with every other hne. It is also possible 
to arrange groups of social phenomena in series according 
to their degree of complexity or according to any other 
standard, even though evolution has not actually taken 
place according to that series. 

If, therefore, we are to assume that human social phe- 
nomena are of the highest type, it does not follow that all 
lower types have been in the same evolutionary series. In 
order to determine the series for man, it is necessary to 
determine to what organic series he belongs, and the series 
for social phenomena will correspond in large part, if not 
entirely, to the organic series. 

M. Petrucci in his suggestive monograph on the relations between 
animal societies which has already been cited discusses this point 
so well that I cannot do better than to quote from him : "We do not 



The Beginnings of Social Evolution 333 

know if the vertebrates are descended from the articulates or from 
another branch of invertebrates; however, each of these branches 
presents in its classes, its orders and its genera phenomena of a social 
order. The same is true for the prochordates which are most closely 
related to the ancient type which was the origin of the vertebrates. 
In the group of the selacians, in which is to be found the existing ex- 
ample most closely related to the type of fish which could have led to 
the continental vertebrates, are to be found social characteristics. 
But it is evident that the divergence of the original stock of the verte- 
brates from that of the existing prochordates, which has separated 
all the fishes of the transitional type leading to the continental verte- 
brates, is very ancient and has not left any precise trace. It is by 
analogy only that we could reconstruct an inherited social character. 
The separation of the vertebrates from the invertebrates has already 
taken place in Silurian time, so that it must have happened in Cam- 
brian time, and since that moment there is no more possibility of a 
direct comparison between animal societies of invertebrates and of 
vertebrates. In the same fashion, the divergent evolution which 
has separated the fishes from the reptiles began as early as Silurian 
time, and since that time there is no more possibility of inheritance 
in a direct line and of a direct comparison between societies formed 
by fishes and those formed by reptiles. The divergence which has 
separated from a common source the three classes of reptiles, mammals, 
and birds must have taken place no later than the end of Permian 
time during the Primary period, because at the beginning of the Sec- 
ondary period are found mammals, reptiles, and traces of birds. 
From that time the direct comparison of societies formed by these 
three classes is no longer justified. In the next place, within the 
mammals themselves the orders of monotremes and of marsupials, 
differentiated from a common source, can no longer be compared 
directly. The other orders of mammals, the rodents, carnivora, and 
herbivora, differentiated from a t3^e which they share with man, 
have been able to inherit a common social tendency, but have varied 
from it in different ways which destroy all possibility of direct com- 
parison. In the last place, in the direct Hne to man the lemurs are 
in the same position as the marsupials and monotremes, and it is 
only with the apes belonging to the order of primates, that is to say, 
with the anthropoids, that societies formed by man could be most 
narrowly compared. However, the divergence, at this point also, 



334 The Science of Human Behavior 

having displayed itself from the starting point furnished by a primate 
previous to the pithecanthropus ape, direct comparison is no more 
possible. We arrive, therefore, at this conclusion: the polyphyletic 
origin and the direct non-comparability of animal societies ^ ^ 

However, even though human society is not in the same 
evolutionary series with any other animal society now in 
existence, it is still worth while to study these other societies, 
and such study will throw light upon the evolution of 
human society. This is true, in the first place, because 
while these species, including the human species, may not 
have inherited in common an associative tendency, they 
have inherited in common certain structural forms and other 
characteristics which have deternimed in part and have 
conditioned the social phenomena displayed by all these 
species. In the second place, all these species have been 
subjected to a certain extent to the same conditions, so that 
their social characteristics are in part due to similar en- 
vironmental conditions. So it is that similar structural 
forms and functions, such as those of nutrition, reproduction, 
etc., on the one hand, and similar environmental conditions, 
such as topography, climate, distribution of food, etc., 
have produced along divergent lines of organic evolution 
social phenomena which are to a certain extent similar. 
As we shall see, the same is true of mental phenomena, and 
to study either the mental or the social phenomena of any 
species is to throw light upon the corresponding phenomena 
of any species possessing them. The preceding statements 
will explain why this chapter is entitled the beginnings of 
social evolution, for social evolution, like mental evolution, 
has had many beginnings along widely divergent lines of or- 

^ Op. cit., pp. 31-32. 



The Beginnings of Social Evolution 335 

ganic evolution, and yet there have been many analogies and 
likenesses between these different Hnes of social evolution. 
I have already spoken of the way in which the food quest 
brings together members of the same species when their 
food is distributed over a small area. As organic evolution 
progresses, the reproductive needs play a more and more 
important part as a cause of association. We have seen in 
an earlier chapter that at the beginning of organic evolution 
organisms were in large part, if not entirely, independent in 
their power to reproduce. That is to say, in the case of 
most, if not all, individuals reproduction could take place 
simply by fission. But comparatively early, if not from the 
very start, conjugation became necessary between certain 
individuals. That is to say, it became necessary for in- 
dependent lines of descent to cross occasionally, or else they 
would lose the power of reproduction. Conjugation in 
these low species probably takes place usually as the result 
of chemo tropic attraction. Here, then, was a force bringing 
members of the same species into contact with each other. 
Then gradually, as we have seen, among the lower metazoan 
species began to arise the anatomical and physiological 
differentiation between the two sexes. When the physio- 
logical division of labor in reproduction based upon this 
differentiation became firmly established, cooperation be- 
tween the two sexes became almost invariably necessary for 
reproductive purposes. In the higher species there de- 
veloped a combination of reflexes which we call the sexual 
instinct and which has ever since been a cause for asso- 
ciation along many divergent lines of evolution. In this 
instinct we find a common heritage of all species that have 
started on a line of social evolution. 



336 The Science of Human Behavior 

But as organic evolution continued, more than the sexual 
instinct became necessary for reproduction to be effected 
successfully. As animal forms developed and became more 
complex, more time was needed for the development of the 
individual animal from the beginning of its life to its full 
development. During a part, at least, of the time needed 
for attaining maturity the animal was helpless and in need 
of care. Thus there developed the parental instincts 
leading one or both parents to care for the young during 
this period of helplessness. Where the care is given by 
one parent, more usually it is the female, though sometimes 
it is the male, as in the case of many fishes and certain 
birds. From parental care there results association between 
parents and their young which, when it becomes more or 
less permanent and stable, is called the family. In these 
instincts we again find a common heritage of most, if not all, 
species that have started on a Hne of social evolution. 

As the nervous system, and especially the central nervous 
system, evolved, the anatomical basis for the development 
of intelligence was furnished, as we have seen in the last 
chapter. The differentiation of the nerve cells from the 
other somatic cells began very early among metazoan spe- 
cies, but the development of the nervous system has taken 
place along many divergent fines of evolution. Wherever 
the nervous system has developed in such a fashion as to 
make association possible, intelligence has become possible 
and has therefore made its appearance along many divergent 
lines. Wherever it has made its appearance and has de- 
veloped to any extent, it has become a powerful force for 
association in various ways. It has made members of a 
species susceptible to suggestion from members of the same 



The Beginnings of Social Evolution 337 

species and has thus led them to imitate. It has enabled 
members of a species to consciously recognize other members 
of the same species as such. It has enabled members of 
the same species to communicate with each other and has 
thus enabled them to conserve ideas, etc., by transmitting 
them from one generation to another in the form of tradi- 
tion. In the anatomical basis of intelligence, then, we find 
still another common heritage of most, if not all, speci-es 
that have started on a Une of social evolution. 

I have now indicated very briefly the different types of 
forces which give rise to association ; namely, certain 
characteristics of the environment, such as the distribution of 
food, temperature, climate, etc., certain inborn character- 
istics, such as the sexual and parental instincts, and certain 
acquired characteristics comprised under the head of in- 
telligence, which is made possible by an inherited anatomical 
structure. There is not enough space in the remaining 
chapters to present all the data with respect to the begin- 
nings and early stages of social evolution along the many 
divergent lines of evolution, even though these data are 
still very Umited in comparison with the number and dif- 
ficulty of the problems involved. Some of these data are 
paleontological and furnish evidence, in the form of fossils 
distributed in small areas, of association on the part of 
extinct species. But most of these data are with respect 
to living species representing many divergent lines of 
evolution. I shall therefore only discuss briefly the data 
with respect to a few species representing different parts of 
the animal kingdom with the hope that such discussion will 
throw some Hght upon the causes for the beginnings of 
social evolution and the forces which determined the charac- 
ter of the early stages of this evolution, 
z 



CHAPTER XVIII 

INSECT SOCIETIES I THE ANTS 

Anatomical polymorphism, 339. — Physiological division of labor, 
339. — The philoprogenitive instincts,. 342. — The founding of an 
ant community, 343. — The food-procuring activities, 345. — The 
hunting stage, 346. — The agricultural stage, 347. — Harvesting, 347. 

— The pastoral stage, 347 . — Symbiosis, 347 . — Parasitism, 351. — Myr- 
mecophilism, 351. — CommensaHsm, 351. — Slave making, 357. — The 
intelligence of ants, 359. — The ant brain, 359. — Recognition, 360. 

— Communication, 362. — Suggestion and imitation, 362. — Coopera- 
tion, 363. — Insect societies are based mainly upon instincts, 363. 

Among the invertebrates the insects have gone furthest 
along the road of social as well as mental evolution, as illus- 
trated by the ants, bees, social wasps, etc. I shall there- 
fore discuss briefly the social phenomena of the ants, since 
they display what is probably the greatest range of such 
phenomena among the insects. 

It is well known that ants live in large communities 
numbering sometimes, it has been estimated, hundreds of 
thousands of individuals. Their nests, in the form of hills, 
subterranean passages, etc., require in their construction a 
high degree of concerted action. It may appear, therefore, 
that they must be endowed with a high degree of intelligence, 
and this has been the opinion of many people in the past. 
But a more careful examination of the ants and their be- 
havior shows that most of these social activities can be 
explained without the aid of intelligence. 

338 



Insect Societies: the Ants 339 

Polymorphism 

The first thing to be noted is the morphological or ana- 
tomical polymorphism which characterizes the ants. All 
species above the asexual stage are characterized by sexual 
dimorphism. But there are certain species in which one 
or both of the sexes appear under two or more distinct 
forms. Such polymorphism is to be found in what is 
perhaps its most fully developed form in the social insects, 
such as the termites (which are sometimes called the white 
ants, though they are not at all related to the ants), in which 
both sexes are equally polymorphic, and the ants, social 
bees, and wasps, in which usually the female alone is differ- 
entiated into distinct castes. Sexual dimorphism makes 
possible a division of labor so far as reproduction is con- 
cerned. Polymorphism permits of a much more extended 
division of labor, which is frequently similar to the division 
of labor which characterizes human society. But human 
division of labor is largely intelligent in its origin, while 
division of labor based upon polymorphism is not necessarily 
accompanied by intelligence. Such division of labor is 
termed physiological and is due to congenital differences of 
structure, which necessarily involve different modes of be- 
havior. 

The question of the origin of polymorphism is an im- 
portant one in this connection, but I shall discuss it only 
very briefly, in the first place, because it is still unsettled, 
but more particularly for lack of space. Wheeler in his 
valuable discussion of this subject suggests that it may have 
resulted from a physiological division of labor, in the follow- 
ing words: "Polymorphism is of rare occurrence in the 



340 The Science of Human Behavior 

animal kingdom and may be said to occur only in colonial 
or social species where its existence is commonly attributed 
to a physiological division of labor." ^ And again he speaks 
more particularly of its origin in the group of insects to 
which the ants belong. ^'This restriction of polymorphism 
to the female in the social Hymenoptera, with which we are 
here especially concerned, is easily intelligible if it be trace- 
able, as is usually supposed, to a physiological division of 
labor, for the colonies of ants, bees, and wasps are essentially 
more or less permanent families of females, the male repre- 
senting merely a fertiHzing agency temporarily intruding 
itseh on the activities of the community at the moment it 
becomes necessary to start other colonies. We may say, 
therefore, that polymorphism among social Hymenoptera 
is a physical expression of the high degree of social plas- 
ticity and efficiency of the female sex among these insects. 
This is shown more specifically in two characteristics of 
the female, namely, the extraordinary intricacy and ampH- 
tude of her instincts, which are thoroughly representa- 
tive of the species, and her ability to reproduce partheno- 
genetically." ^ It is, however, difficult to believe that 
polymorphism could have resulted from a physiological 
division of labor, for this would be putting the function 
before the structure it characterizes. In fact, it seems quite 
necessary that polymorphism should exist before a physio- 
logical division of labor could be possible. It seems more 
probable that polymorphism must be due either to deter- 
minants in the germ plasm which stand for the different 
castes or differences in the conditions under which the 

» W. M. Wheeler, Ants, their Structure, Development and Behavior, New York, 
1910, pp. 86-87. * Op. cit., p. 87. 



Insect Societies: the Ants 341 

young develop. Both of these theories have been proposed 
and discussed. For example, Weismann advocated the 
germ plasm theory, as might be expected. Many of those 
who have held the other theory have believed that the 
differences between the different castes are due to differ- 
ences in nutrition ; that is to say, differences either in the 
quantity or quahty of the food given to the young. This 
last theory seems to be the most plausible one, but nothing 
certain is as yet known, as is indicated in the following 
passage: ^'We may conclude, therefore, that while the 
conception of the worker phase as the result of imperfect 
nutrition is supported by a considerable volume of evidence, 
we are still unable to understand how this result can take 
on so highly adaptive a character. Such a concise effect can 
hardly be due to manifold and fluctuating external causes 
like nutrition, but must proceed from some more deeply 
seated cause within the organism itself. Of course, the 
difficulty here encountered is by no means peculiar to 
polymorphism; it confronts us at every turn as the all- 
pervading enigma of living matter." ^ 

However, whatever may have been the origin of polymor- 
phism, the important part it plays in the social life of ants 
is very evident. The division of labor based upon it causes 
a high degree of interdependence within the ant com- 
mimity. The pol3nnorphism exists principally within the 
third or worker caste, which are females which are sterile, 
apparently owing to the lack of food. The males are few 
in number and are usually very stable. The females are 
relatively stable, but less so than the males. The workers 
are very unstable and appear in many species in many differ- 

1 Wheeler, op. cit., p. 109. 



342 The Science of Human Behavior 

ent forms, each being fitted by structure to perform a 
peculiar function. 

Philoprogenitive Instincts 

The part played by the philoprogenitive instincts in the 
social Ufe of the ants must be noted next. In fact, it is 
probable that these instincts have formed the strongest 
force for social evolution among the ants. WHieeler in- 
dicates their importance in the following words: ^'In 
the lives of the social insects the threptic or philoprogeni- 
tive instincts are of such transcendent importance that all 
the other instincts of the species, including, of course, those 
of alimentation and nest building, become merely trib- 
utary or ancillary. In ants, especially, the instincts 
relating to the nurture of the young bear the aspect of a 
dominating obsession. Their very strength and scope ren- 
der the insects more susceptible to the inroads of a host 
of guests, commensals and parasites." ^ It is difficult to 
explain why the philoprogenitive instincts are so strong 
among the ants. The ancestors of the ants were solitary 
in their habits. They must have developed philoprogeni- 
tive instincts to a certain extent, otherwise their ofifspring 
would not have survived. But some of their descendants 
have developed these instincts much less than the ants, as, 
for example, the wasps, which do not see their offspring at 
all, having buried the egg with a caterpillar or other animal 
as food for the larva to feed upon after it has hatched. 
The ants, on the contrary, care for the young for a long time 
after hatching and in many different ways. This may be 
due to the fact that the young of the ants pass through four 

^Op. cit., p. ii8. 



Insect Societies: the Ants 343 

stages before they mature. These stages or ins tars are 
known as the egg or embryo, the larva, the semipupa or 
pseudonymph, and the pupa or nymph. This high degree 
of complexity in the ontogenetic development of the ant 
probably explains in part the polymorphism of ants, for by 
lack of nutrition or in some other way the development of 
the ant can be arrested at certain points. As each of these 
stages needs special care of its own, the philoprogenitive 
instincts have to be developed very greatly for the preserva- 
tion of the species. 

Let us trace very briefly the founding of an ant com- 
munity. A female, having been fertilized at the time of the 
nuptial flight, becomes dealated by rubbing off its wings. 
It then seeks for a convenient spot for founding its nest in a 
protected place. Having found it, perhaps under a large 
stone, it shuts itself in from the external world, and in course 
of time begins to lay eggs. During all the period of egg 
laying it does not go out for food, but lives off the nutritive 
matter which is stored up in its wing muscles. When the 
first eggs are laid, the female, or queen as it is usually called, 
cares for them and the young which are hatched from them 
until they mature. So far the group constitutes no more 
than a family. But now is manifested the phenomenon 
which is to make the group far more extensive and complex 
than a family. The workers which appear are sterile as a 
rule, as has been indicated. But they have apparently 
inherited some philoprogenitive instincts from their mother, 
for instead of leaving the nest to live by themselves or to 
found a new nest, they go out to forage for food, which they 
bring back to the nest and feed to the brood and to the 
queen. In many other ways they manifest these instincts 



344 The Science of Human Behavior 

by caring for the brood. Thus we have the singular spec- 
tacle of these worker ants, thwarted from breeding them- 
selves because of the arrested development of their repro- 
ductive organs, lavishing a parental care upon their fellow 
offspring. Held, therefore, to the maternal nest by these 
philoprogenitive instincts and enabled by the polymorphism 
which characterizes every species of ants in varying degrees 
to differentiate their activities, the family group founded 
by the queen develops into a vast community carrying on 
extended social activities. 

The importance of polymorphism and the philoprogenitive in- 
stincts for the evolution of ant society has been weU stated by Wheeler 
in the following passage: "Owing to this preestabUshed structure 
and the specialized functions which it imphes, ants are able to Hve 
in a condition of anarchistic socialism, each individual instinctively 
fulfilHng the demands of social Ufe without 'guide, overseer, or ruler,' 
as Solomon correctly observed, 'but not without the imitation and 
suggestion involved in an appreciation of the activities of its fellows. 
An ant society, therefore, may be regarded as Httle more than an 
expanded family, the members of which cooperate for the purpose of 
still further expanding the family and detaching portions of itself to 
found other famihes of the same kind. There is thus a striking 
analogy, which has not escaped the philosophical biologist, between 
the ant colony and the cell colony which constitutes the body of a 
Metazoan animal; and many of the laws that control the cellular 
origin, development, growth, reproduction, and decay of the individual 
Metazoan, are seen to hold good also of the ant society regarded as 
an individual of a higher order. As in the case of the individual 
animal, no further purpose of the colony can be detected than that 
of maintaining itself in the face of a constandy changing environment 
till it is able to reproduce other colonies of a like constitution." ^ 

* Op. cU., pp. 6-7. 



Insect Societies: the Ants 345 

Food-procuring Activities 

The part played by intelligence in the social life of the 
ants will be discussed later. I wish now to speak of the 
part played by external forces. Inasmuch as ants Hve on 
land and are inured to varying conditions, they are not 
restricted to narrow limits of temperature and of atmos- 
pheric pressure. But the distribution of their food supply 
is for them, as for every species, an important factor in deter- 
mining the extent to which their life is to be social. Species 
whose food is scanty and scattered are forced to live more 
or less solitary lives. Predatory animals, also, such as the 
mammals, birds, and insects of prey, are likely to be soHtary 
in their habits, because hunting can usually be carried on 
best alone. Vegetarian species, on the other hand, are 
likely to be social, because their food is usually abundant 
and is more or less concentrated in places where conditions 
are favorable for its growth. The family of the Formicidae 
which the ants constitute was formerly carnivorous. Of 
the five subfamilies of this family only the two lower, the 
Ponerinae and the Dorylinae, are now purely carnivorous. 
And it is a significant fact that these subfamihes have less 
permanent and complex societies than the other three. 
The colonies of the Ponerinae are rare and of small size. 
The colonies of the Dorylinae, though sometimes very large, 
are of a nomadic character, since they must always be seek- 
ing new hunting grounds in order to secure enough food. 
The ants of the three higher subfamilies, the Myrmicinae, 
the Dolichoderinae, and the Camponotinae, though some- 
times predatory, have become adapted to a more varied 
diet, and some of them hve almost entirely on vegetable 



346 The Science of Human Behavior 

food. These subfamilies have developed the most stable 
and complex societies among the ants.^ 

The food-procuring activities of the ants present a series 
of very interesting and significant phenomena which have 
been interpreted by some as indicating a high degree of 
intelligence on the part of the ants. But it is probable that 
these activities can be explained in the main on other than 
intelligent grounds, though intelligence may play a small 
part in them. I will describe briefly some of the principal 
activities. 

Three economic stages have been distinguished among the 
ants corresponding to similar stages among men. These 
are the hunting, pastoral, and agricultural stages. The 
activities which characterize each of these stages have been 
described by some observers in such a way as to seem to 
imply that they involve nearly, if not quite, as much intelli- 
gence as among men. But a more careful examination of 
the data seems to indicate that they involve much less 
intelligence than among men. The lowest stage among the 
ants, as among men, is the hunting stage. It has already 
been indicated that the two lower subfamilies of the For- 
micidae are the hunting ants and that these are less de- 
veloped socially than the other ants. The tendency to hunt 
is largely an instinctive matter among the ants, as it is 
among all animals. That the hunting of ants involves 
much less intelligence than the hunting of men is indicated 
by the fact that ants do not use weapons, though this differ- 
ence may be accounted for by differences in structure. 

Among men the pastoral stage usually succeeds the hunt- 
ing stage. But among the ants the pastoral stage involves 

» Cf. W. M. Wheeler, op. cit., pp. 176-177- 



Insect Societies: the Ants 347 

more complex phenomena than the agricultural stage and 
seems to display the exercise of more intelligence, so that I 
will discuss the agricultural stage first. The agricultural 
stage is exhibited by the so-called harvesting ants, which 
store seeds in granaries in their nests. This practice is 
probably largely the result of instincts which may be closely 
related to the philoprogenitive instincts. Food which is 
not needed immediately is set aside to be used later in 
feeding the brood. But some observers have claimed that 
certain species not only store away food in this fashion but 
also plant seeds and cultivate the crop which grows from 
them. If this were true, it would be difficult to explain it 
solely on the basis of instinct and would seem to involve a 
degree of intelligence almost equal to human intelligence. 
But it seems quite clear that this is not the case. The 
observers who have claimed this have based their assertion 
on the fact that some of the hills of the harvesting ants are 
surrounded by a ring of the kind of plants from which they 
harvest their seeds. But the presence of this ring is in all 
probability purely accidental so far as the ants are con- 
cerned. It is probably due to seeds that have been dropped 
by ants on their way to the nest and to seeds in the chaff 
which has been rejected. Some of these seeds sprout and 
take root and thus in course of time a field of these plants 
grows up around the hill.^ 

Symbiosis 

Let us now turn to the so-called pastoral stage as ex- 
hibited by the ants. This brings us to a subject which I 
wish to discuss in this connection, namely, that of associa- 

1 Cf. W. M. Wheeler, op. cit., pp. 286-287. 



348 The Science of Human Behavior 

tion between members of different species. So far I have 
been discussing only association between members of the 
same species or at any rate between members of closely 
related species. But there are various kinds of association 
between animals which are more or less different, and these 
kinds of association must be considered in studying the 
origin and evolution of society, for they have played some 
part in social evolution. Relations of a symbiotic character 
also exist between animals and plants which are of great 
importance for both. Such relations exist in the case of 
certain species of ants. But inasmuch as plants have no 
mental characteristics, such relations can never become 
social in the strict sense of the term. Mental interaction 
can, however, exist between members of different animal 
species, and social relations can therefore become estab- 
lished between them. It goes \^dthout sa}dng that the extent 
to which such mental interaction can exist and such social 
relations can be established varies more or less directly 
with the degree of difference between species. The mental 
interaction may take place in the form of suggestion and 
imitation. Parental care may be lavished by an adult of 
one species upon the young of another species, thus estab- 
lishing a social relationship similar to that between parents 
and offspring. This is not surprising when the species are 
more or less aHke, as when a hen adopts some ducldings, 
but it is surprising when they are very different, as in the case 
reported by Lloyd Morgan where a hen adopted some young 
ferrets. Such a thing can happen, of course, only when 
parental feeUng is strong in the adult so that it is prone to 
give vent to it by caring for the first young and helpless of 
any species which it happens to meet. We shall see a little 



Insect Societies: the Ants 349 

further on that ants misdirect their philoprogenitive in- 
stincts in this fashion sometimes. 

The term pastoral when used among men is applied to the 
activities of man in caring for animals in flocks or herds 
which have been domesticated by him and which he is going 
to use usually as food or from which he is going to procure 
food. Let us see what activities among the ants correspond 
to such pastoral activities among men. Certain species 
of ants secure much of their food from certain insects which 
secrete juices from plants, which they excrete in the form of 
a liquid like honey and which the ants like very much. 
Among these insects are the plant lice (Aphididae), scale 
insects or mealy bugs (Coccidae), tree hoppers (Membraci- 
dae), lantern flies (Fulgoridae), jumping plant lice (Psylli- 
dae), and the caterpillars of the Lycaenid butterflies. The 
symbiotic relations which become established between the 
ants and these insects are most evident in the case of the 
aphids, so I will speak of them. The aphids excrete their 
honey from the anal orifice in the form of drops. The ants 
caress them with their antennae, and this stimulates them to 
evacuate the honey. The aphids seem to like the caressing, 
so that there becomes established a symbiotic relationship 
which is mutually profitable to both kinds of insects. But 
the aphids profit in still other ways from their relations 
with the ants. The ants protect them from insects which 
prey upon them. These insects, of course, seek the aphids 
for a reason similar to that of the ants, namely, to secure food. 
But many of them would kill the aphids if they succeeded 
in reaching them, instead of simply taking from them an 
edible product, as the ants do. So that the protection of the 
ants is very useful to the aphids. Then many of the aphi- 



350 The Science of Human Behavior 

dicolous ants construct small inclosed pavilions, or sheds, 
which serve for the protection of the aphids as well as of 
themselves. Many observers have thought that these sheds 
are built for the express purpose of housing the aphids; 
but it is more likely that they are constructed as the result 
of an instinct which leads them to excavate tunnels and 
chambers around roots, and then the aphids are brought 
there because the ants can feed from them more conveniently 
there. So that the protection afforded the aphids by these 
constructions is an accidental and unintentional result. 
Aphidicolous ants also sometimes collect and store aphid 
eggs in their nests, bringing up the young aphids after 
they have hatched. This has seemed to some observers a 
purposeful raising of these aphids in order to secure food 
from them after they have matured. But it is quite prob- 
able that this is a case of misdirected parental care, such 
as I have already discussed. 

It is sometimes said that the aphids are the cows of the 
ants and it is true that there is something of an analogy 
between the relation of aphids to ants and that of cows to 
men. But it is an analogy that should not be carried too 
far, as I believe the above considerations show. Cattle 
were originally wild and had to be tamed and domesticated 
by man before he could make use of them for securing food 
in the form of milk. But the aphids seem to be very docile 
creatures, and it is very doubtful if the ants ever had to 
domesticate them. It goes without saying that intelli- 
gence does not have to be assumed to explain why the ants 
eat the honey which falls from the aphids. The caressing 
of the aphids in order to induce them to evacuate the liquid 
may be an acquired habit and may indicate a small amount 



Insect Societies: the Ants 351 

of intelligence, a connection in the associative areas haying 
become established between the act of caressing and the 
securing of food. But even this practice of the ants may be 
due to some obscure instinctive tendency which we do not 
understand. As we have seen, the constructing of sheds 
and the bringing up of the young of the aphids are probably 
due to instincts with which we are familiar. So that it 
seems quite evident that the analogy between the pastoral 
stage among men and the so-called pastoral stage among 
the ants is in the main a superficial one and is principally 
an analogy between external appearances. However, this 
so-called pastoral stage furnishes a highly interesting ex- 
ample of a symbiotic relationship between widely different 
species from which both benefit and which is therefore 
worthy of study. 

In their relations with the aphids and the other insects 
mentioned above the ants assume an active r61e and are to 
a certain extent parasitic upon them. But the ants have 
certain other symbiotic relations with other animals in 
which the ants are usually either passive or indifferent. 
In these relations the other animals force themselves upon 
the ants and become either parasites upon them or com- 
mensals with them. These animals when they inhabit 
ant nests either throughout hfe or during one or more of 
their developmental stages are called myrmecophiles or 
ant guests. Inasmuch as myrmecophihsm illustrates para- 
sitism and commensaHsm I shall describe it briefly. 

Wasmann and Escherich have estimated that there are 
over three thousand myrmecophilous species, including 
a large number of Arthropoda, of which more than a thou- 
sand are beetles, a certain number of Arachnida, and a few 



352 The Science of Human Behavior 

Crustacea. Wasmann, who has studied myrmecophilism 
more than any other investigator, has classified the myrme- 
cophiles as follows : — 

1. Inimically persecuted intruders, or synechthrans. 

2. Indifferently tolerated guests, or synoeketes. 

3. True guests, symphiles, or myrmecoxenes. 

4. Ecto- and entoparasites. 

The fact that there are so many myrmecophilous species 
indicates that ant nests must be attractive to small ani- 
mals. Wheeler gives several reasons for this attractiveness. 
''In the first place, the nests are usually permanent abodes 
inhabited for months or years by successive broods of ants. 
Second, these nests have at all seasons a slightly higher 
temperature than the surrounding soil. Third, there is 
usually more or less refuse food or offal, pupal exuviae, 
and dead ants, at least in the superficial chambers. Fourth, 
the living larvae and pupae represent an abundant and 
highly nutritious food supply for any insects that can elude 
the watchfulness of the ants. Fifth, the ants, in protecting 
themselves from larger animals, necessarily protect any 
small organisms Kving in their nests. Sixth, the philo- 
progenitive instincts of the ants are capable of being de- 
ceived and exploited, for these insects are so fond of nurs- 
ing that they are always ready to lavish their affections on 
any organisms that resemble ant larvae. Since the dwell- 
ings of termites, social wasps, and bees offer many of the 
attractions here enumerated, it is not surprising to find that 
these insects, too, have their nest mates and parasites." ^ 

The first class of myrmecophiles mentioned above, the 
synechthrans, are not very numerous. They live in ant 

• Op. cit., pp. 379-380. 



Insect Societies: the Ants 353 

nests as scavengers and kill isolated ants. The ants drive 
them from the nest whenever possible. 

The second class of myrmecophiles, the synoeketes, live 
in the ant nest either because they are not noticed by the 
ants or because they do not arouse great animosity. They 
are not noticed by the ants when they are too small, too 
colorless, or too slow of movement to be perceived, or when 
they have no specific odor which distinguishes them from 
their environment. In the case of some of the synoeketes 
the ants cannot seize and hold them because of their ana- 
tomical structure and therefore cannot remove them from 
the nest. Some synoeketes pay no attention to the ants 
or their brood, seeking only the refuse in the nest, and are 
therefore left unmolested by the ants. Some of them de- 
velop mimetic characteristics which make them resemble 
the ants themselves or symphiles. Some synoeketes per- 
form services for the ants as, for example, strigilating them. 
But these synoeketes are very nearly if not quite symphiles, 
which I shall discuss next. 

The symphiles, or true guests, which are very largely 
beetles, Hve on amicable terms with the ants in their nests. 
The ants lick them and feed them and frequently care for their 
eggs. The ants hck the symphiles apparently because they 
are very fond of the secretion which oozes from these crea- 
tures. The symphiles stroke the ants with their antennae, 
and this seems to stimulate them to regurgitate food, per- 
haps because they mistake this stroking for similar treat- 
ment from their fellow ants, and this stroking stimulates 
the instinctive tendency to regurgitate. The caring for 
the eggs of the symphiles by the ants is apparently an ex- 
pression of their philoprogenitive instincts. ^'The philo- 
2a • 



354 The Science of Human Behavior 

progenitive instincts are quite sufficient to account for the 
phenomenon, which is merely a parasitic disease, or in- 
stinct aberration, comparable to the rearing of the young 
cuckoo by its foster parents, or the rearing of puppies by 
cats, of kittens by hens, etc. In these cases we do not 
postulate a special hereditary instinct modification, but a 
simulation of the normal stimulus by an abnormal object. 
The instinct action is normal, but adapts itself to the 
changed conditions, and there is nothing to indicate that 
the instinct disposition has undergone any philogenetic 
change." ^ The caring for the symphiHc eggs is indeed to 
the detriment of the ants, for the larvae of the symphiles 
and indeed the symphiles themselves frequently eat the 
ant brood, and it is only the great reproductive powers of 
the ants which preserve them from extinction. This in- 
dicates that the caring for the symphihc eggs and young by 
the ants is the result of a bhnd instinctive tendency, not 
the result of intelligence. Further indication of this is that 
the ants, after burying the symphihc larvae as they bury 
their own larvae, dig up as many of them as they find at 
the time of pupation. But while this is the right thing 
for their own pupae, it usually results in the death of the 
symphiHc pupae. So that the caring for the symphihc 
young by the ants results in injury to the symphiles in some 
cases, when these young are killed off, and when they sur- 
vive it may result in injury to the ants themselves because 
the symphiles may eat the ant brood. 

The ectoparasites and the entoparasites are still more 
dependent upon their hosts than the symphiles. The 
ectoparasites are small creatures that Hve on the outside 

* W. M. Wheeler, op. cit., p. 411. 



Insect Societies: the Ants 355 

of the ants, feeding off of them in various ways. The 
entoparasites are either still smaller creatures which live 
inside of the ants or they are the larvae of fhes and other 
animals which are hatched inside the ants, from which they 
emerge later, sometimes not before they have killed their 
hosts. 

These symbiotic relationships of the ants which have 
just been briefly described vary greatly as to the ex- 
tent to which they furnish the basis for association in 
the sociological sense of that term. It is doubtful if there 
could ever be any mental interaction in a purely parasitic 
relationship. A thoroughly parasitic species is usually 
very Httle developed in many of its parts, and this would 
be true of the parts which determine the mental charac- 
teristics. For the pure parasite the host is probably never 
anything more than a source of food and of warmth. But 
in the relations of the ants with the symphiles there is 
possibility for a certain amount of mental interaction. 
They may influence each other's behavior to a certain 
extent by means of suggestion, imitation, etc. The same 
is probably true to a lesser degree of the relations of the 
ants with the synoeketes and the S3niechthrans. The same 
might also be true of the relations of the pastoral ants 
with the aphids and other species exploited by them, but 
this is very doubtful because of the very low mental de- 
velopment of the exploited species. 

These symbiotic relations displayed by the ants appear 
in many divisions of the animal world. Parasitism is a 
very widespread phenomenon. In fact it is quite likely 
that the majority of Hving species are either parasites or 
the hosts of parasites. However, as I have indicated, 



356 The Science of Human Behavior 

parasitism is not of much significance for association and 
social evolution. The other symbiotic relations appear 
less frequently. The highest type of such relationship and 
the one which is of most significance to us is the relation 
between man and the animals that he has domesticated. 
Here we find what is without any doubt the highest degree 
of mental interaction between different species which has 
been developed anywhere in the animal world. 

There is still another form of symbiosis manifested by 
the ants which must be mentioned here. This is the 
symbiosis between ant colonies of different species. It has 
already been indicated that the ants constitute the family 
of the Formicidse, which includes a very large number of 
species. Under this form of symbiosis are also included 
usually similar symbiotic relations between ant colonies 
and colonies of termites. These cases of symbiosis are 
usually classified under the heads of compound nests and 
mixed colonies. ''Different species of ants or of ants and 
termites are said to form compound nests when their 
galleries are merely contiguous or actually interpenetrate 
and open into one another, although the colonies which 
inhabit them bring up their respective offspring in different 
apartments. In mixed colonies, on the other hand, which, 
in a state of nature, can be formed only by species of ants 
of close taxonomic affinities, the insects live together in a 
single nest and bring up their young in common. Although 
each of these categories comprises a number of dissimilar 
types of social symbiosis, and although it is possible, under 
certain circumstances, as will be shown in the sequel, to 
convert a compound nest into a mixed colony, the distinc- 
tion is nevertheless fundamental. It must be admitted, 



Insect Societies: the Ants 357 

however, that both types depend in last analysis on the 
dependent, adoption-seeking instincts of the queen ant 
and on the remarkable plasticity which enables allied 
species and genera to live in very close proximity to one 
another. By a strange paradox these peculiarities have 
been produced in the struggle for existence, although this 
struggle is severer among diiBFerent species of ants than 
between ants and other organisms." ^ 

The symbiotic relations established under this form of 
symbiosis are very varied. Two or more colonies of dif- 
ferent species of ants or of ants and termites may locate 
their nests in contiguity or in close proximity by chance. 
If in going and coming they meet frequently, they may 
influence each other a good deal and thus the symbiotic 
relation may mean something. If, however, they do not 
meet very much, the relation may mean very Httle. If 
their nests become connected by galleries, they will mingle 
a good deal and thus influence each other a good deal. 
Sometimes a nest is located near another nest for the pur- 
pose of marauding its inhabitants. There is not the space 
to describe all the different kinds of relations which develop 
between different species of ants or between ants and 
termites. But one very extraordinary practice of certain 
species must be described briefly. I refer to the so-called 
slave making carried on by certain species. By this phrase 
some observers have meant that these ants consciously 
make slaves just as we have seen it has been thought that 
the pastoral ants consciously domesticate the aphids and 
other animals. But we shall see that these slave-making 

* W. M. Wheeler, op. cit., 423-424. 



358 The Science of Human Behavior 

practices are not carried on for the purpose of making 
slaves but as the result of certain instincts. 

It sometimes happens that a queen ant in search of a 
nest will enter the nest of another species and will succeed 
in forcing the workers in this nest to adopt her and to bring 
up her young. In such a case the queen and her young 
become temporarily and sometimes permanently parasitic 
upon the original inhabitants of the nest. But this can 
hardly be called a case of slave making. As we have al- 
ready seen, certain species are in the habit of raiding the 
nests of other species and stealing their young. This is prob- 
ably due primarily to hunger. But the philoprogenitive in- 
stincts inherited from the queen may have something to do 
with it, for the females sometimes steal eggs from other nests 
evidently for the purpose of rearing the young which will 
hatch from them. At any rate some of these eggs and 
young are usually eaten. Those that are not eaten are 
reared with the young of their captors and become per- 
manent members of the nest. If this was all, then the cap- 
ture of these eggs and young would simply have resulted 
in the formation of a mixed colony. But some of these 
species have a tendency to become dependent and para- 
sitic upon these ahen ants which they have captured. In 
some cases they become so dependent that they would 
perish without the care of their so-called slaves. The 
causes for the development of this parasitism are very 
obscure. But it seems quite evident that beyond the 
force used in capturing them there is no compulsion exer- 
cised over the alien ants in the nest, so that the term slave 
is a very inaccurate one to apply to them. 



Insect Societies: the Ants 359 

Intelligence 

Before closing this discussion of the social behavior of 
the ants I must discuss briefly their intelligent characteris- 
tics. It was stated in the last chapter that it may not be 
legitimate to speak of association where there is no mental 
interaction and that no society can evolve without such 
interaction. Several times in the course of this discussion 
of the ants it has been suggested that under certain cir- 
cumstances mental interaction may exist between ants in 
the form of suggestion, imitation, etc., and also between 
ants and other animals. It is very difhcult to secure data 
with regard to such mental interaction in the case of ani- 
mals so small as the ants. It is only by observing varia- 
tions in their behavior that we can conjecture as to how 
they are being influenced by others. However, I will 
summarize some of the evidence with respect to this point. 

As we have seen in previous chapters, no variations in 
behavior which can be called intelligent or conscious can 
take place unless there are association areas in the brain, 
and therefore there can be no mental or psychic phenomena 
without such association areas. If this is true, it is evident 
that there can be no mental interaction without such asso- 
ciation areas. It is therefore necessary to investigate first 
the nervous system of the ants in order to determine 
whether they possess the necessary neural basis for mind. 

The frontal lobes of the ant brain consist of two pairs of structures 
called the pedunculate or mushroom bodies, each of which is a cup- 
shaped mass of nerve fibers connected with the rest of the brain by a 
stem formed of similar fibers. The results of the investigations of 
several of the students of these bodies are briefly summarized in 
the following passage which I shall therefore cite : "It has been cus- 



360 The Science of Human Behavior 

tomary since the time of Dujardin to compare the pedunculate bodies 
with the cerebrum of vertebrates and to regard them as an organ of 
intelligence. Dujardin based his opinion on the fact that these bodies 
are largest and most elaborately developed in the social Hymenoptera. 
Leydig and Rabl-Ruckard expressed a similar opinion. Forel (1874) 
first observed that these bodies are largest in worker ants, smaller in 
the queens and vestigial in the males, and as the worker was supposed 
to be the most, and the male the least, intelUgent, this was regarded 
as additional evidence in favor of Dujardin's opinion. The condi- 
tion described by Forel for the ants was affirmed by Brandt (1876) 
for the social Hymenoptera in general. More recently Kenyon 
(1896), after an elaborate study of the bee's brain, has reached a 
similar conclusion. He says : * All that I am able at present to ofifer 
is the evidence from the minute structure and the relationships of 
the fibers of these bodies. This seems to be of no inconsiderable 
weight in support of the general idea started by Dujardin. For in 
connection with what was made known by Flogel and those before 
him and has since been confirmed and extended by other writers, 
one is able to see that the cells of the bodies in question are much more 
speciaUzed in structure and isolated from the general mass of nerve 
fibers in those insects where it is generally admitted complexity of 
action or intelligence is greatest.' He also cites experiments of Binet 
(1894) which tend to show that in insects 'when connections between 
the dorso- and ventro-cerebron are destroyed, the phenomena after- 
wards observed are similar to those seen in a pigeon or mammal when 
its cerebral hemispheres are removed.'" ^ 

These facts seem to indicate that the ant has associa- 
tion areas and that they compare favorably with those of 
other insects. We may therefore expect to find that the 
ant is characterized by mental phenomena and manifests 
variations in behavior of an intelligent sort. I will speak 
of a few of these which are of significance for the social 
life of the ants. 

The ants display the ability to recognize nest mates and 
aliens, and it seems quite evident that this is not an in- 

* W. M. Wheeler, op. cit., pp. 54-55. 



Insect Societies: the Ants 361 

herited reflex, but is acquired. This is indicated by the 
facts that, on the one hand, ants can learn to accept ants 
of other species as nest mates, as is the case in mixed 
colonies and compound nests, and, on the other hand, that 
ants that have been separated as pupae from their own 
colony will treat members of it as enemies. This could 
not be the case if ants inherited the tendency to treat 
only the members of their own species as friends and others 
as enemies. It is quite evident, therefore, that the recog- 
nition is due to an acquired habit of association, and there 
is a good deal of evidence that the recognizing is accom- 
plished through the sense of odor. This is indicated by 
the experiment which has been performed of bathing an 
ant in the blood of crushed ants from another colony and 
then placing the ant back in its own nest, when it was 
attacked by the members of its own nest. Wasmann, who 
has studied this question at great length, expresses his 
opinion as follows: ''The amicable reaction of ants to the 
odor of their own colony is not innate, but is acquired 
individually by the single ants. This individual acquisi- 
tion occurs during the period in which the young, freshly 
developed worker begins to harden and take on her adult 
coloration. During this period her own definite individual 
odor first develops, and during this period there develops 
in her antennae the olfactory sense, by means of which she 
is able to distinguish the odor of her own nest mates from 
those of other ants. Hence the ant's abihty to distin- 
guish between 'friend' and 'enemy' does not depend on 
inherited reflexes, but on the sensory perception of the 
olfactory impressions she receives during the first days of 
her life as an imaginal worker." 



362 The Science of Human Behavior 

Most observers believe that ants are able to communi- 
cate with each other. This seems to be indicated by the 
way in which they will gather at a place where one of 
them has found food or will retire from a place where some 
of their number have been killed or injured. To be sure, 
these phenomena may be explained in such a way that it 
is hardly accurate to speak of them as cases of communi- 
cation. For example, an ant coming from food may leave 
the odor of it along her trail, by following which ants will 
find the food. Certain sounds and movements made by 
ants seem to convey meanings to other ants, or at least to 
influence their behavior. Some of these are vibrations of 
the antennae, movements of the jaws, butting with the 
head, stridulation, etc. Furthermore, ants display their 
desire that their fellows act in a certain way by coercing 
them, as when they drag their queens about by the man- 
dibles or carry one another to a nest or back to the old 
nest. There is great danger of interpreting these move- 
ments and sounds in too anthropomorphic a fashion. It 
is inconceivable that any of them have the conceptual sig- 
nificance that is possessed by words and sentences in human 
language. Probably most of them are instinctive in their 
character. But they influence the behavior of their fellows 
in a way which is almost, if not quite, intelligent in its 
character. Thus they are probably similar in their effects 
to the emotional cries in higher animals, which frequently 
influence behavior greatly. 

I have spoken several times of the possibility that sug- 
gestion and imitation take place among ants. Many 
observers think that they have observed imitation among 
ants. This seems to be the case when a few individuals 



Insect Societies: the Ants 363 

begin acting in a certain fashion and soon others begin 
acting in similar fashion, and this continues until the whole 
community is acting in the same way. It appears frequently 
as if the more initiative and alert members begin to act in 
a certain way and then are imitated by the others. This 
happens when a new condition faces the group and has to 
be met by some new form of behavior which may be de- 
vised by one or more of these more intelligent individuals. 
Thus we see the phenomena of invention and leadership 
displayed in a very rudimentary way. 

Cooperation is frequently observed, and this may some- 
times be the outcome of communication and of imitation. 
But it must be remembered, as has already been shown, 
that most of what appears to be cooperation among the 
ants is the result of a physiological division of labor and of 
common instinctive tendencies. 

Still other aspects of the mental equipment of ants have 
been studied, as, for example, their memory and their 
capacity for learning by experience. All these characteris- 
tics are of some significance for their social behavior, but 
there is not the space to discuss them here. This chapter 
has shown that association among the ants is caused prin- 
cipally by anatomical polymorphism, which results in a 
physiological division of labor, and by certain instincts, 
especially the philoprogenitive instincts. The same is true 
of all the social insects. In the species which are not poly- 
morphic association is caused in the main by certain in- 
stincts. 

This description of the social characteristics of the ants 
must suffice as illustrating social phenomena among the 
invertebrates. 



CHAPTER XIX 

VERTEBRATE SOCIETIES 

Paleontological evidence of association among vertebrates, 364. — 
Fishes, 365. — Amphibians, 370. — Reptiles, 371. — Difiference be- 
tween cold- and warm-blooded vertebrates, 372. — Birds, 373. — 
The famUy, 374. — Mammals, 376. — Primates, 384. — Man, 387. 

Let us now make a brief survey of social phenomena 
as they appear among the vertebrates. In doing so, special 
attention will be given to the mammals, because man is a 
mammal. 

There is some paleontological evidence that vertebrates 
have been social for a long time. This evidence is in the 
form of fossil remains distributed over small areas, which 
fact seems to indicate that when these remains were de- 
posited, these species were Hving in bands and groups. 
These remains go far back in geological time, some of them 
dating from secondary time, while there are fossils dating 
from primary time indicating social Hfe, but it is not certain 
that any of these are vertebrate. Such evidence with 
regard to the past is, however, necessarily very fragmentary. 
Most of the evidence must be secured from the study of 
living forms. But this evidence is of significance with 
respect to the past as well as for the present. If we find 
that social phenomena characterize species which are 
widely separated, and these phenomena are in part due to 
characteristics which are common to these species, we 

S64 



Vertebrate Societies S65 

have some reason for believing that these social charac- 
teristics must have appeared in part at least before the 
point of divergence between these different Hnes of descent. 

Fishes 

The lowest class of the vertebrates consists of the fishes, 
so that we will consider first the social life of the fishes. 
Many species of fish five in shoals, frequently including a 
large number of individuals. In fact, some observers assert 
that this is true of most fishes.^ This may be due in part 
to certain external forces which have been mentioned in 
a preceding chapter ; namely, temperature, pressure of the 
water, distribution of food, etc. But it is doubtful if these 
forces can explain it entirely in most, if in any, cases, for the 
area favorable for the Hfe processes of the fishes is usually 
much larger than the area covered by one of these shoals, 
so that there must be still another force bringing them to- 
gether. It is difficult to observe fishes in their natural 
habitat, so that explanations of their social behavior must 
necessarily be somewhat conjectural in their character. The 
fishes have only a slight mental development, owing to the 
slight development of the association areas of their brains. 
So that it is doubtful if there is much mental interaction 
between them. 

But the sexual instinct is strong at certain seasons of the 
year, and the parental instinct appears to a sHght extent in 
some species. When the sexual instinct manifests itself, 
it may bring the two sexes together. It, or rather certain 
curious instincts which sometimes accompany it, in cer- 
tain species, causes them to do other things at the same 

1 Cf. Brehm, Les merveilles de la nature, les poissons, Paris, p. 43. 



366 The Science of Human Behavior 

time. For example, in the case of certain salt-water species 
just previous to the breeding time the males and females 
accompany each other up a river sometimes for a long dis- 
tance to a place where the eggs are laid and hatched. The 
origin of these instincts is very obscure, but their utility 
to the species is very evident, since the young are much more 
likely to survive if born in the quiet waters of a river rather 
than in the sea or ocean. These instincts cause associa- 
tion between the sexes during this journey up the river. 
Most species of fish are oviparous, so that bodily contact 
is not necessary in order to impregnate the female. But 
bodily contact and rubbing between the sexes seems to 
take place sometimes and may stimulate the flow of milt 
from the male and of ova from the female. Since this takes 
place when the two are in close proximity to each other, 
the two fluids are almost certain to mingle, and some of 
the ova may be impregnated. 

Out of the 8000 or more species of fish there are about 
180 species which are viviparous.^ In these species the 
male has to come into bodily contact with the female in 
order to impregnate it, or at any rate it has to come near 
enough to inject its spermatozoa into the vent of the female. 
Then there are many species in which the male and female 
need never see each other. The female leaves its ova in 
the water. A male of the same species is attracted to them 
by their odor, and, instead of eating them, as it might the 
ova of another species, it sheds its milt over them, thus fer- 
tihzing some of them. 

The above indicates very briefly the kinds of associa- 

^ Alexander Sutherland, The Origin and Growth of the Moral Instinct, London, 
1898, p. 36. 



Vertebrate Societies 367 

tion between the sexes at breeding time. Let us now con- 
sider parental care among the fishes. There is very little 
of such care, especially on the part of the female. There 
appear to be only about ten species in which there is any 
maternal care, and in each of these cases the care is by 
means of an anatomical structure which serves to a certain 
extent as a sort of substitute for viviparity, so that maternal 
care is only to a very sKght extent conscious. For example, 
in the six species of Aspredo the flat belly of the female 
becomes soft at breeding time. After the eggs have been 
fertiHzed by the male, she rolls upon them so that they 
stick to her, and she carries them in this fashion until they 
are hatched. In a few species the female has a pouch in 
which she carries her eggs until they are hatched. In the 
viviparous species the eggs are hatched either in the ovary 
or in the oviduct, there being no uterus or womb. In a 
few cases there seems to be a slight amount of maternal care 
after birth. 

There is therefore very little maternal care among the 
fishes, and paternal care is more characteristic of them. 
The probable reason for this is that in most species the 
male fertilizes the eggs after they have left the female, 
and is therefore the last of the two parents to concern it- 
self with them. As has been indicated, it is peculiarly 
sensitive to the smell and perhaps also to the sight of the 
eggs of its own species, and the attraction they have for it 
is sometimes strong enough to keep it with the eggs until 
they are hatched. During this time it cares for them in 
various ways. In some species it simply drives away ma- 
rauders who would otherwise eat the eggs. In other species 
it takes the eggs into its mouth and carries them until 



368 The Science of Human Behavior 

they are hatched. The males of some species have pouches 
or soft bellies in which to carry the eggs, like the females 
which have already been described. 

But the highest form of parental care displayed by the 
fishes is nest building, and the best example of this is found 
among the sticklebacks. The male stickleback builds his 
nest of weeds, straws, twigs, and leaves, sticking them to- 
gether with mucus from his belly and weighting them with 
sand. Then he goes in search of a female, which he drives 
into the nest and keeps there until she has laid her eggs. 
He then watches over the eggs for from ten to thirty days 
until they are hatched, after which he protects them until 
they are able to wander off by themselves. 

We see, then, that among the fishes are to be found varia- 
tions from no parental care whatever to a certain amount 
of care. But in no case is there any association of any im- 
portance between parents and offspring, because, as has 
been indicated in the species which displays the most care, 
the young leave the father very soon, and the association 
before the separation takes place is of a very instinctive 
sort and therefore involving very little, if any, mental inter- 
action. But this parental care is indirectly of great im- 
portance for social evolution. In the first place, it must be 
evident that where there is no parental care there must be 
an enormous waste of eggs, while as the degree of parental 
care increases the number of eggs needed to preserve the 
species will steadily decrease. This is well illustrated in 
the case of the fish. "Of species that exhibit no sort of 
parental care, the average of forty- nine gives 1,040,000 
eggs to a female each year ; while among those which make 
nests or any apology for nests the number is only about 



Vertebrate Societies 369 

10,000. Among those which have any protective tricks, 
such as carrying the eggs in pouches or attached to the body, 
or in the mouth, the average number is under looo ; while 
among those whose care takes the form of a uterine or quasi- 
uterine gestation which brings the young into the world 
alive, an average of fifty-six eggs is quite sufficient." ^ 
In the second place, when there is parental care the period 
of helpless infancy can be lengthened, and the individual 
can develop to a higher stage before becoming mature. 
This is especially true with respect to the brain and 
nervous system, which will evolve in a more or less direct 
proportion to the degree of parental care.^ This more 
highly evolved nervous system will furnish the basis for 
more association and higher types of association. 

It must now be evident that the life of fishes does not 
exhibit much association or high types of association be- 
tween the sexes or between parents and offspring. There 
still remains the association in large shoals which has already 
been mentioned. This form of association is apparently 
not due to the sexual or parental instincts. It probably 
does not involve much mental interaction. It might be 
due to such an associative tendency or gregarious instinct 
as we have already discussed. But, as we have seen, the 
existence of such a tendency or instinct must be regarded 
as very doubtful. It may be that this form of association 
is due to a habit of associating together acquired by the 
young immediately after hatching, when, owing to the 
circumstances of their birth, they are thrown into each 

1 Sutherland, op. cit., p. 40. 

2 This is illustrated among the fishes by the fact that most of the viviparous 
species belong to the shark order, and the sharks have the largest brains in propor- 
tion to their weight of any fish. 

2b 



370 The Science of Human Behavior 

other's company. However, so far we can only con- 
jecture as to the causes for this form of association dis- 
played by fishes, and it is to be hoped that more study will 
be made of their behavior so that we may understand better 
the causes of the social phenomena displayed by these ani- 
mals. 

Amphibians 

The next class to be considered is that of the amphibians 
or batrachia, which includes such animals as frogs, toads, 
salamanders, newts, etc. Here we find much the same 
social phenomena as among the fishes. Perhaps the prin- 
cipal difference is that in most of these species the male 
clasps the female more or less tightly for a day or two at 
breeding time. The sexes are probably attracted together 
at this time by odor. The clasping is probably a stereo- 
tropic reaction due to irritation of the skin of the breast of 
the male at this time, which needs contact to allay it. Males 
have been known to clasp stones, sticks, etc., at this time, 
so desperate is their need to put themselves in contact with 
something. One great advantage arises from this reaction. 
When the female releases her ova, the male squirts his 
spermatic fluid over them so that the eggs stand a good 
chance of being fertilized. This increases the chances for 
survival, for example, over the fishes, two thirds of whose 
eggs, it is said, rot unfertilized. Some species are vivip- 
arous, in some of them the sperm fluid being sucked into 
the female through the genital opening. There is a little 
parental care, in which respect the batrachia are very 
similar to the fishes. In some species there are pouches 
or soft bellies in which the eggs are carried until hatched. 



Vertebrate Societies 371 

These anatomical devices for protecting the eggs are some- 
times on the males, sometimes on the females. There is 
very little in the way of nest building. 

Reptiles 

The next class is that of the reptiles, which includes the 
turtles, crocodiles, Hzards, snakes, etc. With the possible 
exception of one genus (Sphenodon) containing two species, 
all reptiles fertilize their eggs internally, which increases 
greatly their chances for subsequent development. There 
is great variation among the different species as to how 
soon after fertilization the eggs are to be laid. Among the 
lower reptiles, such as the tortoises and turtles, the eggs are 
laid almost undeveloped. Among the higher reptiles, such 
as the snakes, the eggs are kept in the oviduct until half or 
three quarters hatched and sometimes until fully hatched. 
Thus the internal fertilization, the tough integument of 
the egg, and the universal reptilian instinct of conceaHng 
the eggs increase greatly the chances that the eggs will 
hatch and thus lessen greatly the number of eggs which are 
needed for the perpetuation of the species. There is very 
httle parental care. It is said that the crocodile returns 
to the place where she has laid her eggs and aids the young 
to escape from them, but this is not certain. Some snakes 
incubate their eggs, but appear to give no care to the young 
after they are hatched, these being able to take care of 
themselves. 

It must now be evident that the amphibians and reptiles 
are very little, if any, above the fishes in social development. 
Sexual relations are very temporary, and relations between 
parents and offspring are almost nonexistent, owing to the 



372 The Science of Human Behavior 

slight amount of parental care. In some amphibian and 
reptilian species, the individual members are sometimes to 
be found congregated together in considerable numbers, but 
whether this is due to social causes or not, it is hard to say. 
In any case there certainly is very Httle mental interaction, 
since the mental development of amphibians and of reptiles 
is very low. 

The Warm-blooded Vertebrates 

We now come to the two highest classes of vertebrates ; 
namely, the birds and the mammals. Both of these 
classes have undoubtedly sprung from a reptilian origin, 
but there is an important difference between them and the 
other vertebrate classes. The other classes are all of them 
cold-blooded ; that is to say, their body temperature is, within 
certain rather wide Umits, approximately the same as that 
of the environing medium. But the birds and the mammals 
are warm-blooded ; that is to say, their body temperature 
is kept by certain internal processes at a rather high point, 
which is usually above that of the environing medium. 
This characteristic of the birds and mammals is undoubt- 
edly of considerable significance for their mental and social 
evolution. The warm-blooded type developed as a result 
of the development of the sympathetic nervous system, 
which regulates the vasomotor system in such a fashion 
as to keep the body at a uniform temperature by sending 
blood where more warmth is needed and stimulating the 
action of the sweat glands where the heat needs to be re- 
duced. I have not the space to discuss the causes for this 
development here. As we have seen in an earlier chapter, 
the emotions arise out of the activity of the sympathetic 



Vertebrate Societies 373 

system, so that the development of that system means the 
development of the emotional nature of these classes, of 
animals. So that the emotions involved in sexual, parental, 
and wider social relationships now begin to play a much 
greater part. 

Birds 

Among birds the eggs are fertilized internally and are 
partially matured inside the female, but are laid before they 
are hatched, so that all birds are oviparous. There is a 
great deal of variation among the birds as to the degree 
of parental care, as in all these other classes. Generally 
speaking, the degree of parental care varies with the degree 
of intelKgence. The least intelligent are the running birds, 
such as the ostrich, the emu, the rhea, and the cassowary. 
These species make no nest beyond digging a hole in the 
sand or soft earth in which the eggs are laid. The incubat- 
ing may be done by both parents, but in many of these 
species is done in large part or entirely by the male, so that 
paternal care preponderates over maternal care among these 
species. This is reminiscent of the lower classes, in which, 
as we have seen, paternal care is frequently predominant. 
There is very little care of the young, since they are almost, 
when not entirely, self-dependent from the time of hatching. 

The next group of birds, which are of medium intelligence, 
includes the web-footed, the stilt-legged, the pheasant-like 
birds, and the pigeons. Some of these species make no 
nests whatever. The others make nests most of which are 
rather rude in character. In all these species the female 
does most of the brooding, but is usually assisted by the 
male. The young are hatched more or less dependent and 



374 The Science of Human Behavior 

have to be cared for during varying periods of time before 
they can shift for themselves. 

The most intelligent birds include the birds of prey, the 
owls, the woodpeckers, the parrots, the sparrow-Hke and 
the finch-like birds. There are 1670 genera of these birds, 
and they all display a great deal of parental care. Most of 
them make nests. Those of them which do not make nests 
lay their eggs in safe places which are sometimes better than 
nests. They display much intelligence in adjusting their 
nests to local conditions instead of invariably building 
them in the same way. The brooding is usually done by 
the female, but the male always remains with her, feeding 
and protecting her. The young are always hatched helpless 
and have to be warmed and cared for in every other way for 
some time by both parents. Even after they are able to 
care for themselves, the young of certain species remain 
with their parents, sometimes until they are ready to mate 
and found homes for themselves. 

Among the birds we see the family making its appear- 
ance. Among the running birds it is very weak. These 
birds are frequently to be found in small groups of males 
and females in which a certain amount of temporary pair- 
ing may take place. Sometimes a single male will be ac- 
companied by several females. But no unions of any 
duration between individuals of the two sexes seem to be 
formed, and, as we have seen, there is Httle parental care. 
Among the birds of medium intelligence the family makes 
its appearance in very definite form. Here we find parental 
care through the period of helplessness by at least one parent 
and frequently by both parents. When the latter is the 
case, we have a union between the two parents which lasts 



Vertebrate Societies 375 

at least as long as the breeding season. Among the birds 
of high intelligence there is always parental care by both 
parents, and very frequently pairing takes place for Hfe. 
Thus we find the monogamous family fully developed 
among the birds, with permanent conjugal relations and 
relations of considerable duration between parents and 
offspring. 

It is hardly necessary to emphasize the significance of 
these conjugal and these parental and filial relationships 
for social evolution. In the course of a long-continued or 
permanent conjugal relationship there can develop a degree 
of cooperation which would not be possible during a brief 
and temporary connection. During such a long connec- 
tion a great deal of mental interaction must necessarily 
take place. We cannot know to what extent the birds are 
able to communicate with each other, but some of their 
notes seem to have specific meanings, while in the form of 
suggestion and imitation there is much mental interaction. 
Then the long-continued relations between the parents and 
offspring must have great influence over the young. During 
this time the young can learn many things from the older 
birds, and thus a certain amount of social tradition in the 
form of ways of doing things, as to what things are to be 
avoided, etc., can be transmitted from generation to genera- 
tion. 

But perhaps the principal social significance of this 
family hfe is that it is a preparation for a wider type of 
association. Many species of birds five in flocks and 
other large groups. In family life is acquired to a certain 
extent the habit of association which fits the young for 
life in the flock. It must be noted, however, that the family 



376 The Science of Human Behavior 

may be, and very frequently is, antagonistic to the wider 
forms of association. The attraction between the sexes 
and the jealousies which arise therefrom frequently result 
in the breaking up of the larger group, so that it is fre- 
quently hard to determine whether the family is more of a 
force for or against the wider forms of association. But 
this is a subject which will be discussed more fully later 
with respect to mammals as well as birds. 

Various forms of social relations arise in these larger 
groups. Cooperation for warning against danger and for 
defense against danger takes place to a great extent. Mi- 
grations usually take place in these large flocks. There is 
a great deal of play in the form of singing, caressing, etc., 
which goes on in these flocks. In the case of most, if not 
all, of the higher birds that do not come together in large 
groups there is some special reason for it. Certain species 
have to maintain solitary habits in order to escape the 
observation of their enemies, just as other species have to 
combine in order to defend themselves against their enemies. 
Certain birds of prey have to live solitary lives in order to 
secure their food, since it would be impossible for a large 
number of them to secure sufilcient food at one place. 

Mammals 

Let us now survey briefly the social characteristics of 
the mammals. As has already been stated, the mammals, 
hke the birds, have a reptihan origin, but it is impossible 
to determine at what point the mammalian hne of evolu- 
tion diverged from the reptilian. This point, however, was 
undoubtedly different from the point at which the avian 
line of evolution diverged from the reptilian. The lowest 



Vertebrate Societies 377 

mammals give indications of their reptilian origin, for they 
are to a certain extent transitional forms. The lowest 
mammahan order is that of the mono tr ernes. This order, 
which includes the duckbill or platypus (ornithorhynchus) 
and the spiny anteater (echidna), is reminiscent of the 
reptiles in several ways. It is not completely viviparous, 
inasmuch as the young are sometimes born while still 
inside the covering of the egg. The young are, however, 
born or hatched weak and helpless and only partially 
developed and not active and independent Hke most of 
the young reptiles. Parental care is therefore absolutely 
necessary for the survival of the young, and this care is 
always maternal. The female has two pouchlike folds 
into which she lifts her young. Inside these pouches are 
glands from which oozes a milky secretion upon which the 
young feed. These are, in all probabiHty, modified fat 
glands which form rudimentary milk glands, though Gegen- 
bauer thought they were modified sweat glands. The 
mother carries her young until they are able to shift for 
themselves. Conjugal relations among the monotremes 
are apparently of the briefest sort, occurring only for the 
purpose of sexual intercourse. There seem to be among 
them no social relations of a wider sort, since they form no 
larger groups and seem to be indifferent to each other when 
brought near together. 

The next higher group of mammals is that of the mar- 
supials. This group includes two orders, the first being 
represented by the opossum and the second by the kan- 
garoo. The mammals in this group are wholly viviparous, 
but the young are born partially undeveloped and are 
placed immediately by the mother in a pouch or marsu- 



378 The Science of Human Behavior 

pium, as it is called, from which the group derives its name. 
Inside this pouch are the mammary glands, from which hang 
long, slender teats, through which the young feeds until it 
is able to leave the pouch. Some of the lower species of 
marsupials lack this pouch, or have it only in a rudimentary 
form. But all of them are viviparous and have mammary 
glands. With regard to conjugal association and wider 
forms of association, the marsupials seem to differ a good 
deal amongst themselves. In most of the species conjugal 
relations seem to be solely for the purpose of sexual inter- 
course, but there are certain species in which pairing for a 
longer period of time takes place. Some of the species are 
somewhat gregarious, while others are quite soHtary. But 
in the gregarious species the social relations seem to be of 
a low order and do not involve much mental interaction. 

We now come to the placentaha, which include most of 
the mammahan orders. These orders are named from the 
placenta in the womb through which the young are 
nourished during the uterine Hfe. The young are always 
born fully developed, but in many orders are very helpless 
and need a great deal of parental care for a considerable 
period of time. The placentaha are divided into the non- 
deciduate and the deciduate orders, and this division has 
some significance with respect to the degree of parental 
care needed. In the nondeciduate orders, which include 
the ungulata, the cetacea, and the sirenia, the period of 
gestation is long and the young are born active and usually 
able to move about, but needing the mother's milk and 
parental protection for some time. In the deciduate 
orders, which include the edentata, the rodentia, the in- 
sectivora, the chiroptera, the carnivora, and the primates, 



Vertebrate Societies 379 

the period of gestation is shorter on the average, but the 
young are born much more helpless, so that they are in 
need of much more parental care. Perhaps owing to this 
greater need for parental care after birth, some of the 
deciduate orders have progressed much farther in social 
evolution than have the nondeciduate orders, though it is 
also true that some of the deciduate orders stand very 
low among the mammals both mentally and socially, as, for 
example, the edentata and the insectivora. 

On account of lack of space, I can touch only very briefly 
upon the social characteristics of these mammalian orders. 
In all of them a certain amount of parental care is neces- 
sary in order to suckle the young and also frequently in 
order to protect and warm them. There is great varia- 
tion among them as to the extent to which they display 
conjugal relations and social relations of a wider sort. 
The edentata and the insectivora, which are of the lowest 
grade mentally, seem to have practically no conjugal rela- 
tions or social relations of a wider sort. The m^arine 
mammals, namely, the cetacea and the sirenia, represented 
by the whales and the porpoises, are gregarious and seem 
to be bound together by strong social bonds within their 
herds, but it is doubtful if they have strong conjugal rela- 
tions. The bats (chiroptera) are gregarious, but appear 
to have no conjugal relations other than that of sexual 
intercourse. The sexes are usually segregated from each 
other in large flocks. The rodents vary greatly amongst 
themselves as to their social characteristics. Conjugal 
relations seem to be very weak among them, the pairing 
usually lasting only during the period of sexual excitement, 
and the male rarely ever taking part in the care of the 



380 The Science of Human Behavior 

young. Some of the genera are gregarious and cooperate 
in digging and building, as, for example, the beavers and 
some of the rabbits, but other genera are quite soHtary in 
their manner of life. 

The order of the ungulata is the highest order of the 
nondeciduate placentaKa. The members of this order are 
usually herbivorous and hoofed. It includes a large num- 
ber of genera, in which are the horse, the ox, the sheep, the 
deer, the elephant, and the rhinoceros. The imgulata are 
almost without exception very gregarious and in their 
natural state live almost always in large herds. This is 
quite in keeping with their manner of securing food, inas- 
much as they are herbivorous and hence are not beasts of 
prey. There is very little in the way of conjugal relations, 
as the males and females live together the year around 
without segregating into pairs. Within the herd, however, 
the males usually take upon themselves the task of pro- 
tecting the females and young. The degree of gregarious- 
ness displayed by the ungulata is very great. Galton has 
given a classic statement of it in his description of the 
South African ox. He says that ''the ox cannot endure 
even a momentary separation from his herd. If he be 
separated from it by stratagem or force, he exhibits every 
sign of mental agony; he strives with all his might and 
main to get back again, and when he succeeds, he plunges 
into its middle to bathe his whole body with the comfort 
of closest companionship." ^ This gregariousness is very 
useful for purposes of protection, since if the ungulate 
attempted to hve a soHtary life it would probably be 
destroyed by a beast of prey. But as Galton points out, 

* Francis Galton, Inquiries into Human Faculty, New York, 1883, p. 71. 



Vertebrate Societies 381 

this extreme gregariousness destroys the self-reliance of 
the members of the herd and thus checks their mental 
development. With the exception of the few that act as 
leaders of herds, these animals act in accordance with the 
movements of the herd. Their craving for companionship 
seems to be due largely to habit and the discomfort they 
experience when separated from familiar things. The 
basis for their gregariousness is negative principally, and 
not positive, as it is to so large an extent with the primates, 
who seek each others' company for what they can do to 
and with each other. 

The next order to be considered is that of the carniv- 
ora. It has been stated that this order belongs to the 
deciduate placentaHa. Therefore its young are born quite 
helpless and have to be cared for during a considerable 
period of time. It is therefore to be expected that strong 
parental feeling will be displayed by this order. And this 
is to be found, at least so far as the mother is concerned. 
In all the genera of this order the female devotes herself 
to the care of her young throughout the period of their 
helplessness and displays a strong affection for them. But 
conjugal relations in this order are very weak and in many 
genera do not exist at all aside from sexual intercourse, so 
that there is very little care of the young by the male. 
Furthermore, there is not very much association of a wider 
sort, since not many of the carnivorous species form packs 
or herds. The gregarious species are to be found princi- 
pally in the families of the dog, the seal, and the walrus, 
while the families of the cat, the civet, and the raccoon, 
and the subfamilies of the badger and the weasel are more 
or less solitary in their mode of life. This lack of gre- 



382 The Science of Human Behavior 

gariousness is probably due to the facts that, as they are 
well armed by nature, they do not have to unite for pro- 
tection, and that as beasts of prey they have to scatter in 
order to find their food. 

But despite the solitariness of the manner of Hfe of most 
of the carnivorous species, they display a good capacity for 
leading a social life when the opportunity of leading one 
is offered them. This is indicated by the fact that many 
household pets domesticated by man have been carniv- 
orous animals. I need not stop to describe the social 
characteristics of the dog and the cat, while many other 
carnivorous animals have been domesticated almost, if not 
quite, as successfully, as, for example, the raccoon, the 
badger, the weasel, the seal, etc. This seems like a curious 
fact and is one which it is perhaps a little hard to explain. 
At least two reasons for this phenomenon can, however, be 
indicated, and these may be sufficient to explain it satis- 
factorily. In the first place, it must be noted that the car- 
nivora usually give birth to several offspring at the same 
time, so that there are several young ones being brought 
up at the same time in the lair. As soon as they are old 
enough to do so, they begin to play together, and in these 
playful relations with their fellow offspring as well as in 
their relations with their parents they acquire social habits 
which they never entirely lose. But in course of time, 
when they are old enough, they have to go out in search of 
food, which results in breaking up this association. Or 
jealousy aroused as a result of the awakening of sexual 
feeling may destroy this association. 

In the second place, and this is probably the principal 
reason for the facility with which they adopt social hab- 



Vertebrate Societies 383 

its, the carnivora undoubtedly form the most intelligent 
mammalian order with the exception of the order of pri- 
mates. This is probably due in large part to their preda- 
tory mode of securing food, which places a high premium 
upon skill and cunning. The carnivora are undoubtedly 
subjected in their natural mode of life to a powerful selec- 
tive process which tends to preserve the more intelligent 
and to ehminate the less intelligent. In this respect they 
are in strong contrast to the ungulata, whose preservation 
depends largely, as we have seen, on their conformity to the 
behavior of the herd. It is therefore not surprising that 
the ungulata are relatively unintelKgent and stupid as 
compared with the carnivora. Its relatively high intelli- 
gence therefore enables the carnivore to adjust itself to a 
social Hfe when it is given the opportunity. It is amenable 
to suggestion and will imitate and enter sympathetically 
into the feelings of those surrounding it. It is of course 
necessary in order that it may do these things that it be 
relieved for the time being from the necessity of securing 
food, for otherwise its predatory instincts will control its 
behavior. Such carnivora as the dog and the cat, which 
have been domesticated for many centuries, have been put 
through a long selective process which has weeded out the 
unsocial and has preserved the social. This accounts in 
part for the social characteristics of these animals. But 
there must have been a basis upon which to build in the 
case of these animals, for a totally unintelligent animal 
could not possibly be domesticated, inasmuch as it would 
be incapable of learning. Furthermore, carnivores of other 
species are constantly being domesticated from the wild 
state so successfully as to establish very close relations 



384 The Science of Human Behavior 

between them and their human masters. This suggests 
the part which may be played by intelhgence in making 
animals social. This appears more fully in the highest 
order of mammals, the primates, and will be discussed more 
fully in the next chapter. 

Primates 

We now come to the order of the primates, which is of 
peculiar interest to us, inasmuch as it includes man. The 
period of gestation is on the average much longer in this 
order than it is in any other order. The young are born 
more helpless than in any other order. Consequently the 
maternal instinct is highly developed in this order. Owing 
to the long period of gestation and of infancy, the nervous 
system develops greatly, thus making possible the intel- 
lectual development which furnishes a basis for the high 
degree of social evolution attained by this order. 

The order of primates is usually divided into two sub- 
orders; namely, the lemuroidea and the anthropoidea. 
The lower suborder, the lemuroidea, contains about a 
dozen genera, including the true lemurs (family lemuridae), 
the aye-aye, and the tarsius spectrum. The young of the 
lemurs are not as helpless at birth as those of the other 
primates. For example, immediately after birth they are 
able to climb up the mother's body to the teats, which are 
located on the breast. This pectoral location of the 
mammary glands, which is rare in other orders, is of some 
significance in the primates, for it enables the mother to 
hold her young in her arms while it is suckling, thus in- 
creasing the degree of care and protection she can give it. 
The young must, however, be fed and protected for some 



Vertebrate Societies 385 

time before it can shift for itself, consequently the maternal 
feeling is very strong. It is hard to determine to what 
extent conjugal relations exist among the lemuroidea. It 
is said that the two lowest genera, the aye-ayes and the 
tarsius spectra, are generally found in pairs. But most 
of the lemuroidea are very gregarious and live in groups of 
considerable size in their arboreal haunts. So that it is 
doubtful if conjugal relations are very strong among them. 
They are not very intelligent as compared with the rest of 
the primates, so that there is probably not very much 
mental interaction between them. 

The suborder of the anthropoidea includes five families : 
the hapalidce, which includes the marmosets ; the cebidcBj 
which includes the howling monkey, the squirrel monkey, 
the spider monkey, the capuchin monkey, etc. ; the cer- 
copithecidcEy which includes among others the baboons and 
the macaques ; the simiidce, the members of which are fre- 
quently called the anthropoid apes, which includes the 
gibbons, the orang-utans, the chimpanzees, and the gorillas ; 
and the hominidcBj which includes only man. 

The first three families are monkeys with tails, the first 
two being platyrrhine and the third being catarrhine. To- 
gether they form the lower group of the anthropoidea. 
All of these monkeys of the three lower families are very 
gregarious, and most of them live in groups of different 
sizes. Perhaps for this reason conjugal relations are not 
very strong, but the males seem to have a strong affection 
for the young and protect and care for the young of their 
groups. Polygyny exists among some of these monkeys, 
and the connection between the male and his wives is usu- 
ally permanent. 
2c 



386 The Science of Human Behavior 

The simiidae or anthropoid apes are more like man than 
any other living beings. The infant ape is the most help- 
less of all new-born animals, with the exception of the 
human babe. Consequently, maternal affection is strong 
in all the genera of this family, and the mother cares for 
her young for a long period of time. The lowest genus is 
that of the gibbons (hylobates). These apes hve in bands, 
sometimes numbering as many as one hundred. It is not 
certain whether the sexes Hve in pairs within the band or 
not. But in any case the males share in caring for the 
young. It is said that when on the march the young are 
borne by adults of their own sex. That is to say, a young 
male is carried by a male adult, while a young female is 
carried by its mother. It is hard to explain this curious 
custom. The next genus (simia) contains only one species, 
the orang-utan. It is not very gregarious, since it is ap- 
parently never seen in large groups. The male seems to 
lead a soHtary life usually, but it is said by some observers 
that he keeps near the mother and her young and watches 
over their safety. The chimpanzee (anthropopithecus or 
troglodytes) Hves in small bands and seems to have a highly 
developed capacity for social feeling, as is revealed when it 
is domesticated. The males watch over their mates and 
their young with great care. The gorillas (gorilla) are 
never found in groups, except when a few young gorillas 
are joined together apparently before they have mated. 
A male and female with their young are usually found 
together. Sometimes a male has more than one female. 
The relations between mates and parents and offspring 
seem to be very close. Despite its reputation for fierce- 
ness, the gorilla seems to have a strong capacity for affec- 



Vertebrate Societies 387 

tion, which has been revealed on the few occasions on 
which it has been tamed. 

Man 

The last family of the anthropoidea is that of the homin- 
idae, which brings us to man (homo). I shall discuss else- 
where the characteristics of the branches of mankind which 
have progressed somewhat on the road of human social 
evolution. The social characteristics of primitive man it is 
unfortunately rather hard to determine with certainty, in- 
asmuch as there are very few examples of primitive man re- 
maining. The period of gestation is longer in proportion to 
his size for man than it is for any other living being. The 
human infant is perhaps the most helpless of any species and 
needs parental care for a long period of time. Human pa- 
rental instinct is therefore very strong. Primitive men ap- 
pear usually to have Hved in small groups ranging in size 
from twenty to forty or fifty and perhaps sometimes larger. 
Within these groups there seems always to have been a 
relative degree of promiscuity. But upon the basis of this 
promiscuity there has sometimes arisen monogamy and 
sometimes polygyny, very rarely if ever polyandry among 
the most primitive men. Thus it appears that primitive 
man was more gregarious than the anthropoid apes, with 
the possible exception of the gibbon, and that conjugal 
relations were not usually as strong among primitive men 
as they are among some of the anthropoid apes, as, for 
example, the gorilla, and as they are among some of the 
higher birds. This would seem to relate man with respect 
to his social characteristics more closely to the monkeys 
than it does to the anthropoid apes. This may be corre- 



388 The Science of Human Behavior 

lated with the fact that in his physical characteristics man 
may in some ways be more closely related to the monkeys 
than he is to the anthropoid apes. If this is true, it would 
be due to the fact that man diverged from the main stem 
of the primates at a point nearer the monkeys than the 
apes. However, this is very uncertain, but it seems to be 
the opinion expressed by Petrucci in the following passage : 
** Hence it is that the examination of the animal types 
which have differentiated from the Hne of evolution which 
leads from the primatoid prototype to man shows that 
the lemurs, using these as a type of comparison, display 
life in bands and grouping by families, that this much-accen- 
tuated social characteristic is continued in the monkeys, 
which diverge from this hne, that it is still continued in 
man, while in the anthropoid apes it tends to disappear 
and is clearly displayed only by the gibbons, who resemble 
in this respect the monkeys. Therefore man and the 
gibbon occupy each a place by himself in the heart of the 
order of primates, and man shows himself to be less diver- 
gent from the primitive primate and primatoid type in 
his social characteristics than the other anthropoids (except 
the gibbon). This is in accordance with the place that 
his structure gives him and from this very general pre- 
dominance, even in divergent types, of the social charac- 
teristic from which only certain anthropoid apes escape 
we can conclude for the present that these tendencies are 
inherited in man from the primatoid prototype for which 
the lemurs furnish us a standard of comparison." ^ 

Even if it be true that in some of his physical charac- 

* Origine polyphyUtique, homotypie et non comparabiliU directe da sociMs ani- 
males, Brussels, xqo6. 



Vertebrate Societies 389 

teristics man resembles the monkeys more than he does 
the apes, this does not necessarily mean that he is inferior 
to the apes. As a matter of fact, his brain development 
is much superior to that of the apes, and in an earher chap- 
ter have been discussed some of the reasons for this su- 
periority, though we cannot know all these reasons. On 
account of this superior brain development, as well as for 
other reasons, the Hne which diverged from the common 
primate stock and evolved into man has progressed much 
further mentally and socially than the Hne which diverged 
from the common stock and evolved into the anthropoid 
apes. 



CHAPTER XX 

THE FACTORS OF SOCIAL EVOLUTION 

The causes of association, 390. — ^ The polyphyletism of animal 
societies, 391. — Utility for survival as a controlling factor in 
social evolution, 392. — The reasons for man's superior social evolu- 
tion, 393. — Environmental forces for association, 395. — Instinctive 
forces for association, 395. — Is there a gregarious instinct ? 395. — 
The sexual instinct, 396. — The reproductive instincts, 397. — The 
parental instincts, 397. — The utihty of parental care, 397. — Con- 
jugal relations, 399. — The family, 399. — Wider forms of association, 
401. — The antagonism between the family and the horde, 403. — 
The family as preparing the way for wider forms of association, 404. 
— Emotional forces for association, 406. — Intelligent forces for as- 
sociation, 407. — Imitation, 407. — Recognition, 407. — Communica- 
tion, 409. — Language, 409. — The formation of categories, 411. — 
Meeting places, 414. — Leadership, 415. — Theories of social evolu- 
tion, 416. — Theory of the instinctive origin of society: Petrucci, 
McDougall, 417. — Theory of the emotional origin of society : Adam 
Smith, Sutherland, 418. — Theory of the intellectual origin of so- 
ciety : Giddings, Kropotkin, Tarde, Durkheim, 420. — The com- 
plexity of the factors in social evolution, 421. 

In the last two chapters a brief survey has been made 
of the social characteristics of representatives of the prin- 
cipal branches of the animal world. I shall now make an 
attempt to describe the principal forces which caused the 
origin and early stages in social evolution. 

The preceding discussion has shown how manifold have 
been the causes of association. Certainly it is not to 
be attributed solely to one gregarious instinct, if indeed 

390 



The Factors of Social Evolution 391 

such an instinct exists at all. We have seen that there 
are at least four different kinds of causes of association; 
namely, environmental, instinctive, emotional, and intellectual 
causes. The information which has been furnished with 
respect to these causes will be summarized briefly in this 
chapter. 

POLYPHYLETISM OF AnIMAL SOCIETIES 

The preceding discussion has also shown the variations 
in the extent to which Hfe is social, even among species 
which are closely related to each other. For example, we 
have seen that within the family of the simiidae the gibbons 
are very gregarious, while the gorillas lead a relatively 
solitary Hfe. This discussion has illustrated the poly- 
phyletism of animal societies referred to in an earher chap- 
ter. It has shown that social evolution, Uke other forms of 
evolution, is not entirely Knear, but is to a certain extent 
multiple and divergent. It has shown that social evolu- 
tion is not entirely correlated with organic and intellectual 
evolution. This was illustrated by the fact that the order 
of ungulata is more gregarious than the order of carnivora, 
notwithstanding the fact that the carnivora are much more 
intelligent than the ungulata. It was illustrated by the 
fact that many avian species are more social than many 
mammalian species, even though they have not evolved as 
far organically. This discussion has raised the question 
as to the degree of homology and parallelism which exists 
between the phylogeny of animal societies and the phy- 
logeny of the species of the animals which constitute these 
societies. That there must always be a certain degree of 
such homology and parallelism is quite evident, but that 



392 The Science of Human Behavior 

the two phylogenetic series may vary to a considerable 
extent is also quite evident. 

• The Controlling Factor in Social Evolution 

The explanation of these variations is, I believe, to be 
found in the fact that the controlling factor in determining 
whether association is to exist and the extent to which it is to 
exist is its utility for survival. A species is likely to become 
social if social characteristics will aid it in its struggle for 
existence. That is to say, the individuals possessing social 
characteristics will be selected for survival, and thus the 
species will become more and more social. As we have 
seen, there are various ways in which association will aid 
in the struggle for existence. It may aid in securing food, 
or in caring for the young, or as a means of defense against 
enemies. On the other hand, as we have seen, social char- 
acteristics have little or no utihty for many species and fre- 
quently hamper them in the struggle for existence, as, for 
example, predatory animals who need to be alone to secure 
their food, and certain animals whose safety from their en- 
emies depends upon their being as inconspicuous as possible. 

Lloyd Morgan has described very graphically how socia- 
bility depends upon utility in the struggle for existence in 
the following words: "The assertion that the fittest 
are the most sociable animals, that sociability appears as 
the chief factor in evolution, and that unsociable species 
decay, is not likely to be accepted without quaUfication by 
zoologists. What grounds have we for saying that the 
solitary wasps are less fit than the social wasp ? Each has 
a fitness according to its kind. Can it be maintained that 
the unsocial tiger is less fit than the social jackal ? And 



The Factors of Social Evolution 393 

can it be said that tigers, which are reported absolutely to 
swarm in Java and Sumatra, exemplify the decay of an 
unsociable species? Is it seriously contended that the 
hawk, which may be successfully mobbed by a number of 
wagtails, is less fit than his more social assailants ? And are 
the unsocial raptorial birds decaying species ? Such ques- 
tions might be asked by the score. And the answer in 
every case is that the social and unsocial alike are fitted 
to their several states of hfe." ^ 

Reasons for Man's Superior Social Evolution 

It goes without saying that utility for survival has been 
the controlling factor in the social evolution of man just as 
much as in the case of any other social species. Human 
social evolution is no more teleological than any other kind 
of evolution. Man is very social ^ because he is weak as com- 
pared with many species which prey upon him, because his 
young are born very helpless and remain so for a long time, 
and because he has a highly developed nervous system which 
furnishes the basis for a high degree of intelligence, thus making 
possible a high degree of mental interaction, from which result 
a good deal of pleasure and a great deal of cooperation and 
mutual aid in the form of a social division of labor which 
facilitates greatly the securing of food and the other necessaries 
of life. If it had not been for these advantages accruing 
from association, man would not have been social, despite 
the beHef of many that it was preordained that man should 
reach the highest point in mental and social evolution and 
should thereby dominate the rest of the animal world. 
Darwin, in his classic discussion of this subject, has ex- 

* Animal Behaviour, London, 1908, p. 229. 



394 The Science of Human Behavior 

pressed himself as follows: ''In regard to bodily size 
or strength, we do not know whether man is descended from 
some small species, Hke the chimpanzee, or from one as 
powerful as the gorilla; and, therefore, we cannot say 
whether man has become larger and stronger, or smaller 
and weaker, than his ancestors. We should, however, 
bear in mind that an animal possessing great size, strength, 
and ferocity, and which, Hke the gorilla, could defend itself 
from all enemies, would not perhaps have become social; 
and this would most effectually have checked the acquire- 
ment of the higher mental qualities, such as sympathy and 
the love of his fellows. Hence it might have been an im- 
mense advantage to man to have sprung from some com- 
paratively weak creature." ^ 

In order, therefore, to explain fully the social or unsocial 
characteristics of a species, it would be necessary to know 
the whole history of its phylogenetic evolution and all the 
selective forces of its environment to which it has been 
subjected. In other words, it would be necessary to have 
the same information that it is necessary to have to explain 
its anatomical, physiological, and psychological character- 
istics. By saying this, however, I do not mean to imply 
that social evolution is entirely correlated with organic 
and mental evolution, for, as we have seen, owing to forces 
of the environment and other factors, there may be varia- 
tions in the social characteristics of a species which are not 
accompanied by correspondingly great organic and mental 
changes. But inasmuch as there is a general correlation, 
the data furnished by biological and psychological research 
are of the greatest value for making possible a more detailed 
explanation of social evolution. 

^ The Descent of Man, 2d edit., London, 1890, pp. 63-64. 



The Factors of Social Evolution 395 

Environmental Forces 

Let us now review briefly the forces for association which 
have been discussed. The first group is that of the exter- 
nal, environmental forces, such as temperature, the dis- 
tribution of food, etc. Enemies are sometimes included 
among these forces, though these are perhaps social forces 
in an inverted sort of a way, inasmuch as relations with 
enemies may and usually do involve a certain amount of 
mental interaction. These external forces which bring 
about association are sometimes called socializing forces. 
Criticism has been made of this term by some who have 
contended that these forces also are social forces, inasmuch 
as they would not bring about association were it not for 
certain characteristics of the animals upon which they act. 
It is true that a certain temperature will not bring about 
association unless certain animals are adapted to that 
temperature and that a certain kind of food distributed 
over a certain locality will not be a force for association in 
that locaHty unless certain animals are so constituted that 
they can subsist on that food. But notwithstanding these 
considerations, there is still some reason for distinguishing 
between these external forces and the forces for association 
which arise out of the mental interaction of living beings. 

Instinctive Forces 

The next group of forces for association to be considered 
is that of the instinctive forces. I have stated the theory 
of some writers that there is a specific gregarious instinct 
and have indicated the arguments against this theory. It 
is indeed hard to see how such an instinct can exist, because 



396 The Science of Human Behavior 

it is hard to see how it could have come into existence. The 
exposition of the nature of instinct in a previous chapter 
has shown that no instinct is likely to come into existence 
unless it performs some definite service which is of utility 
in the struggle for existence. A fully developed gregarious 
instinct would be of utility to many species, but I do not 
know what forces would nurse it through the early stages 
of its development before it had selective value. It is 
evident that such an instinct would necessarily have to be 
very complex in its character. It would have to be a re- 
action of the whole organism to the whole organism of an- 
other member of the same species. To be aroused, it would 
probably have to be stimulated through several senses. 
So that the first stages of its development would not be so 
likely to have utility and selective value as the first stages 
of simpler instincts. It is barely possible that a gregarious 
instinct might appear as the result of. the combination of 
several simpler instincts, but it is doubtful if this has ever 
taken place. 

But while we may not believe in a specific gregarious or 
herd instinct, still there are a number of instincts which may 
be called gregarious because they cause association. The 
first of these is the sexual instinct. This instinct is aroused 
by very definite stimulations in the form of tactile exci- 
tations, odors, colors, sounds, movements, etc. It has the 
highest selective value because it is essential to reproduction 
and therefore to the preservation of the species. It does 
not, however, always involve association. As we have seen, 
in some of the fish species the two sexes do not need to come 
into association with each other, for the female will release 
her eggs independently of the males, and the sexual instinct 



The Factors of Social Evolution 397 

of the male will be stimulated by the odor of the eggs so 
that he will release his sperm cells. But in many species 
contact or, to say the least, close proximity is necessary 
for reproduction, and in these cases the sexual instinct re- 
sults in association. 

Some writers speak as if there is a specific reproductive 
instinct, but it is very questionable as to whether there is 
any such instinct. The reproductive process is started by 
the sexual instinct and is continued and its success assured 
in many species by the parental instinct. So that we may 
speak of the sexual and parental instincts and of any other 
instincts which aid in the process of reproduction as the 
reproductive instincts. 

The next instinct to be considered is the parental instinct. 
This instinct, however, manifests itself in many different 
forms in different species and frequently involves several 
more or less distinct instincts, so that it would perhaps be 
more accurate to speak of the parental instincts. All of 
these instincts involve care of the young, and we have had 
numerous illustrations of them earHer in this chapter, as, 
for example, nest building, incubating, suckHng, etc. Such 
care involves association between the parents and the young, 
so that these instincts are a force for association. But 
indirectly, also, they are a force for association. As we 
have seen, as parental care increases, the number of eggs 
needed for the perpetuation of the species decreases. This 
is indicated well in the following passage: ''A steady 
diminution in the number of offspring as parental care 
increases is a prime feature of development. In fish, as 
already stated, the average of seventy-five well-distributed 
and typical species is 646,000 eggs, but in the class amphibia 



398 The Science of Human Behavior 

the average of the twenty species for which information is 
to be had, is no more than 441 eggs, while in the class of 
reptiles, the average of thirty-nine species is only seventeen. 
The birds represent a much higher standard, and they, as 
the average of more than 2000 typical species, give only a 
trifle over five eggs per annum for each female. A still higher 
rank is reached in the mammals ; as the average of eighty- 
two t3^ical species they have only 3.2 offspring to each 
female every year, and within the mammals as a class the 
same progressive diminution is to be seen; all the higher 
orders taken together average only 1.3 young ones each 
year, while the apes and mankind do not exceed one every 
two years." ^ 

This reduction in the number of eggs needed for the per- 
petuation of the species results in a great saving of energy 
and of nourishment for these species, and this saving can 
be utilized for the higher development of the species. Pa- 
rental care also makes possible a lengthening of the period 
of infancy, thus making it possible for the individual to 
reach a higher point before maturity. In many species 
this longer period of development results in a more complex 
nervous system, which furnishes a basis for a higher degree 
of intelligence, which in turn makes possible higher forms 
of association. Thus the parental instincts resulting in 
parental care prepare the way for higher forms of associa- 
tion which otherwise could not possibly have come into 
existence. 

^ A. Sutherland. The Origin and Growth of the Moral Instinct, London, 1898, 
VoL I, p. 41. 



The Factors of Social Evolution 399 

The Family 

Let us now turn to the conjugal relations between the 
parents. We have seen that, in order to reproduce, the 
sexes do not have to come together in all species. In many 
species, probably the great majority, the sexual instinct 
manifests itself only at certain times, usually at certain 
seasons of the year. In these species, therefore, the sexual 
instinct acts as a force for association only at this time, which 
is called the rut. Consequently, if the sexes associate the 
rest of the time, it will be due to other forces. We have 
seen that parental care may be exercised by the one or the 
other parent, or it may be exercised by both parents. If it is 
exercised by only one parent, it is of no significance for con- 
jugal relations. But if it is exercised by both parents, it 
may lead to conjugal relations between the same pair 
through a long period of time and sometimes permanently. 
This will be the case when both parents have the same pa- 
rental instincts, which will lead them to do the same things 
at the same time and therefore together. For example, 
this is well illustrated in the case of the nest-building in- 
stinct. At the time of the rut along with the sexual instinct 
is aroused this instinct in both sexes, so that the mating 
of a pair leads both of them to set about the constructing 
of a nest. When the nest is completed and the eggs have 
been laid, there appears the incubating instinct in both 
parents, though it is usually strongest in the female, while 
the male displays more speciaHzed instincts which lead it 
to act as a protector and a purveyor of food. These in- 
stincts are probably of the nature of the chain instincts 
which have been described in the chapters on instinct. 



400 The Science of Human Behavior 

That is to say, the expression of one of these instincts acts 
as a stimulus for the next one, so that a series of instincts 
may manifest themselves as if they formed one instinct. 
So it is that the presence of these parental instincts in both 
parents may lead to conjugal relations lasting through the 
breeding season. Why it is that in some species these in- 
stincts are transmitted to both parents and in other species 
to but one parent is a problem of heredity which cannot be 
discussed here. 

The sharing of the same parental instincts by both par- 
ents may therefore be the explanation of conjugal relations 
lasting through the breeding season. But this does not 
explain the permanent conjugal relations which exist among 
some of the birds and a few of the mammals. As to whether 
or not it is due to an instinct, it is impossible to say. But 
it seems much more Hkely that it is due to a habit of as- 
sociating together which is acquired during the breeding 
season when they are held together by these instincts. It is 
conceivable that among the higher birds and mammals 
there may be a sufficient degree of mental interaction to 
cause personal relations strong enough to hold individuals 
together, even when there is no other force for association 
at work. 

Out of these relations between parents and offspring and 
these conjugal relations there develops the social group 
called the family. There has been some difference of 
opinion as to what constitutes a family, but the majority 
of writers now seem to think that a family is constituted 
whenever a relation of some duration exists between one 
parent and its offspring. The family may therefore con- 
sist of the mother and the offspring, or of the father and the 



I 



The Factors of Social Evolution 401 

offspring, or of both parents and the offspring. In the few 
species in which polygyny exists, the family would con- 
sist of the father and the mothers with their offspring. 
I know of no species other than the human species in 
which there is any polyandry. 

It is evident therefore from the facts stated in the last 
chapter that the family can hardly be said to appear below 
the birds, since there is no relation of any duration to speak 
of between parents and offspring among the reptiles, am- 
phibia, and fishes, or among the invertebrates. But the 
family reaches a high degree of development among the 
birds and mammals. As we have seen, in a good many 
species of birds niating is for Hfe, and the same is true of 
certain mammals. But it is doubtful if there is any species 
other than the human species in which permanent relations 
are maintained between parents and offspring. In all 
other species the young leave their parents when they are 
full grown and are ready to mate, and the recollection of their 
relationship in all probabiHty soon fades from their memory. 
Among men, on the contrary, this relationship is usually 
remembered permanently and has an important influence 
upon social organization. 

Wider Forms of Association 

Let us now turn to wider forms of association than 
the family. As we have seen, there are a good many 
species that live in groups larger than a family. These 
groups vary greatly in size between the different species. 
For example, we have seen that an ant colony may number 
tens if not hundreds of thousands. Fishes and birds live 
in shoals and flocks which may number many thousands. 

2d 



402 The Science of Human Behavior 

Among the mammals the ungulata live in herds which may 
include thousands, and some of the carnivora form packs 
which number hundreds if not thousands. It goes without 
saying that the family must be made up of members of the 
same species. The same is usually true of these larger 
groups, though there are some exceptions in the form of the 
commensal and parasitic associations which have been 
discussed. 

The causes for these wider forms of association have 
already been briefly discussed in this chapter. I wish at 
this point to discuss a little more fully the relations between 
these wider forms of association and the family. It may 
appear most probable that these larger groups are made up 
of families. This is true to a certain extent in some cases. 
For example, a herd of ungulata may be made up in part 
of females who are accompanied by their young whom they 
are suckling until they are able to feed on grass. But aside 
from this temporary relationship between the mothers and 
their young, there is not Ukely to*be anything like a family 
in a herd of ungulata. And the same principle holds wher- 
ever large groups of this sort exist permanently. It may 
sometimes happen that birds of a species which mate per- 
manently may join together temporarily for their migra- 
tions, but it is evident that as soon as they reach their 
breeding ground they must break up into couples in order 
to found their nests. Again, after the young are hatched 
and are somewhat grown there may arise between the young 
of several families a form of association not based upon 
sexual attraction which might develop into one of these 
permanent associations of the wider sort, were it not for 
the fact that when the sexual instincts manifest themselves, 



The Factors of Social Evolution 403 

sexual jealousy will appear and conflicts among the males 
for the possession of the females. If the species in which this 
happens is monogamous in its tendencies, these jealousies 
and conflicts are almost certain to disrupt the larger group. 

Thus we see that the family tends to oppose the forma- 
tion of the larger group. The antagonism between the two 
has been well stated by Espinas in passages which I hesitate 
to translate for fear of failing to convey their exact meaning 
because of his idiomatic style : "L'egoisme domestique 
est d'autant plus imperieux qu'il a pour centre un moi plus 
comprehensif et qu'il y a en lui du devouement. La con- 
science collective de la peuplade ne peut done pas avoir a 
sa naissance de plus grande ennemie que la conscience col- 
lective de la famille." ^ He indicates how the "peuplade" 
may develop and summarizes the antagonism between it 
and the family in the following words : — 

" I. Le seul passage qu'il y ait de la famille a la peuplade 
se trouve non dans les relations du pere avec la mere et de 
ceux-ci avec les jeunes, mais dans les relations des jeunes 
entre eux; 

"2. Meme a I'origine, la famille et la peuplade sont 
antagoniques ; elles se developpent en raison inverse Tune 
de I'autre; 

"3. Le veritable element de la peuplade est Tindividu; 
et Famour d'un toe pour ses semblables en tant que tels, 
ou la sympathie, y est la source de la conscience collective." ^ 

This antagonism between the family and the wider form 
of association which we may call the peuplade is described 
by Petrucci also in the following words: "The family 
therefore is not essential to the formation of societies. The 

1 Op. cit., p. 473. ' Des socUUs animates, Paris, 1878, pp. 46i>-47o. 



404 The Science of Human Behavior 

clan may sometimes be the extension of the family, but in 
certain animal species, as in man himself, it is not always 
the direct Hne of parentage which is at the basis of the 
group. Sometimes, furthermore, the group can be estab- 
Hshed only when the family disappears. There is antago- 
nism between the two elements. Numerous examples of 
this are to be found in certain species of mammals, where 
the females, after being fecundated, gather by themselves, 
w^hile the males form another troop elsewhere. Association 
exists and the family does not exist. The family, therefore, 
cannot be conceived as a social unity. It is not a group of 
families which forms Society." ^ 

But while it may be true that the well-developed family, 
such as the monogamous or polygamous family, may have 
stood in the way of the evolution of the larger group which 
we may call the horde or peuplade, still the family had pre- 
pared animals for life in this group. So that all I have said 
about the part played by the family in developing certain 
instinctive tendencies and sympathetic emotions and in 
laying the basis for the manifestation of intelHgence holds 
true. The family therefore stands in the rather paradoxi- 
cal position of having prepared the way for a higher form 
of association and then having stood in the wa}^ of its ful- 
fillment. 

Lloyd Morgan has discussed very well the part played 
by the family in preparing the way for the higher forms of 
association. He was led to discuss this by certain passages 
in Prince Kropotkin's well-known treatise on mutual aid. 
Kropotkin says ^ in discussing the origin of human society 



1 Les origines naturellcs de la proprUtt, Brussels, 1905, pp. 225-226. 
' Mutual Aid a Factor oj Evolution, New York, igo2, p. 79. 



% 



The Factors of Social Evolution 405 

that anthropology '^has established beyond any doubt that 
mankind did not begin its Hfe in the shape of small isolated 
famines. Far from being a primitive form of organiza- 
tion, the family is a very late product of human evolution. 
. . . Societies, bands, or tribes — not famiHes — were the 
primitive form of organization of mankind and its earhest 
ancestors. . . . None of the higher mammals, save a few 
carnivores and a few undoubtedly decaying species of apes 
(orang-outans and gorillas) , Kve in small famiHes, isolatedly 
straggling in the woods. All others Hve in societies." 
Morgan, in commenting on this, speaks as follows: ''It 
may at once be admitted that in all probabiHty mankind 
did not have its origin in small isolated famiHes. If we do 
not admit this, we must accept the alternative hypothesis, 
that man was developed from an unsocial ancestor. For 
though the biological family is the starting-point of the 
community, it does not of course foUow that wherever there 
is so much coherence between parents and offspring as to 
form a temporary family group, a social community must 
in due course arise. In such unsocial carnivora as the 
tiger, the temporary Hnkage of family Hfe is strong while 
it lasts. But though mankind presimiably originated in a 
prehuman race that had already reached some degree of 
social coherence, there remains behind the question — 
what was the origin of this social group? And to this 
question, Prince Kropotkine, in common with Darwin and 
Espinas, would probably answer without hesitation, that 
the primeval germ of the social community lay in the pro- 
longed coherence of the group of parents and offspring. 
In the unsocial animals the family separates and disinte- 
grates before the offspring mate. But if the family continue 



406 The Science of Human Behavior 

to cohere, the mating of offspring will give rise to the con- 
tinuity of coherence found in the herd, or troop, or tribe. 
For new family groups will be constantly arising before 
the old family groups have ceased to be associated. Thus 
would be afforded more opportunity for tradition than 
among the unsocial animals." ^ 

Emotional Forces 

I have spoken of emotional causes of association. We 
have seen earlier in this book that emotions are states of 
feeling. As such they cannot be direct causes of behavior 
any more than other feehngs. But we have also seen that 
emotions are almost always, if not always, connected with 
instinctive tendencies and are apparently incidental results 
of the manifestation of these tendencies. We have also 
seen that very frequently these emotions seem to influence 
these instinctive tendencies either by reenforcing them or 
by inhibiting them, thus indirectly influencing behavior. 
As I have said in an earher chapter, "it sometimes happens 
that the emotion is strongest when the external act is in- 
hibited, because action usually relieves the organic condi- 
tions which give rise to the emotion. This indicates how 
an emotion may reenforce and strengthen a tendency to an 
action in order to secure the relief which comes through 
action. This is why emotions become powerful factors 
in the determination of behavior." ^ 

Thus we see in what sense emotions may be causes of 
association. The emotions which are usually called sexual 
love and parental love reenforce the instinctive forces 
which bring together members of the opposite sexes and 

* Animal Behaviour, London, 1908, p. 231. > See chapter XV, p. 302. 



The Factors of Social Evolution 407 

parents and offspring. Many other emotions are more or 
less indirectly forces for association, while still other emo- 
tions are forces against association. As intelligence in- 
creases, the higher animals, and especially men, discover 
new modes of behavior by means of which emotions can be 
satisfied. Like other forms of intelKgent behavior, these 
new modes are constituted by combining inherited forms 
of behavior. 

Intelligent Forces 

Let us now review briefly the intelHgent forces at work in 
the family and in the peuplade, or horde, which encourage 
association. I have already discussed the nature of sug- 
gestion and imitation in the chapter on instinct and have 
indicated their social significance at various points in this 
book. It is probably true, as seems to be proved by ex- 
periments made by Professor Thorndike and others, that 
there is very Httle if any reflective imitation among ariimals 
other than men. But there is a certain amount of imitation 
which is intelHgent in the sense described in a previous 
chapter among the higher animals and a great deal of the 
reflex sort which is sometimes called instinctive, but which 
I have shown is not instinctive in the strict sense of the 
word. Imitation causes uniformity of behavior and con- 
certed action, and is therefore an important force for as- 
sociation. It is an effective mode of transmitting habits 
and other ways of doing things from one generation to 
another. 

It must be evident that recognition plays an important 
part in association. The recognition may be of the reflex 
sort which has been described in the case of ants, where the 



408 The Science of Human Behavior 

recognizing is apparently done by means of odor. But 
whether the recognizing be done by odor, sight, touch, or 
sound, the animal reacts favorably to the sensations to 
which it is accustomed and unfavorably to those to which it 
is unaccustomed. So that it will harmonize with a member 
of its own species or social group, but will be hostile to a 
stranger. I have spoken as if this recognition depended 
upon habit, and so it does in large part. But it must be 
remembered that it may also have an instinctive basis to 
a certain extent. That is to say, the animal may inherit 
the tendency to react favorably or unfavorably, as the 
case may be, towards certain sensations. 

So far I have spoken only of the recognition of the reflex 
sort which enables the animal to distinguish between any 
member of its own species or social group and a stranger. 
But some of the higher species also display the ability to 
recognize individuals. One example of this is when a pair 
of animals mate for a period of time or permanently. It is 
evident that in such a case they must distinguish each other 
from other members of the same species. In similar fashion 
parents may come to distinguish their young as individuals. 
But this probably happens only among the higher animals, 
and among them perhaps only occasionally, as has been 
indicated by experiments in which the offspring of a certain 
parent have been removed and other young of the same 
species or sometimes even of another species have been sub- 
stituted for them without the parent apparently discovering 
the difference. Another example of this higher, intelligent 
sort of recognition is where a herd comes to recognize an 
individual as the leader of the herd. There is probably, 
among the higher animals, more or less of this recognition 



1 



The Factors of Social Evolution 409 

of individuals as distinguished from the mere recognition 
of the members of the same group or species. Both kinds 
of recognition are of course based upon differences in sen- 
sory stimulations, but the recognition of individuals is en- 
tirely the result of experience. 

Communication also plays an important part in social 
relations. Speaking of the origin of communication, Lloyd 
Morgan says: "The foundations of intercommunication, 
like those of imitation, are laid in certain instinctive modes 
of response, which are stimulated by the acts of other ani- 
mals of the same social group. These have been fostered 
by natural selection as a means of social linkage furthering 
the preservation, both of the individual and of the group." ^ 
As we have already seen, there are various ways of communi- 
cation, such as touch, motions stimulating the vision, and 
sounds. But sound has proved to be the most effective 
means of communication for reasons which must be ob- 
vious ; namely, because by means of sound communication 
can take place over considerable distances and because 
sounds can be varied to an almost infinite degree to convey 
different impressions and ideas. So that the abihty to 
communicate has depended very largely upon the develop- 
ment of the vocal organs. 

Very few of the fishes and reptiles possess the ability to 
make any sounds, but more of the batrachians are able to do 
so. The birds can make a large number of sounds, owing to 
the high development of their vocal organs. This is in- 
dicated by their singing and by the abihty displayed by 
some birds to imitate human language. Probably none of 
the mammals except man have as highly evolved vocal organs 

* op. cit., p. 193. 



410 The Science of Human Behavior 

as these birds. It is indeed strange that the vocal organs 
are no more developed among the mammals. For example, 
even among the anthropoid apes, who resemble man more 
than any other animals, the orang-utan, the chimpanzee, 
and the gorilla lack well-developed vocal organs. The 
gibbon has the best-developed organs among these apes, 
enabling him to utter musical sounds. And as the gibbon 
is the lowest of the anthropoid apes, it may be that man has 
inherited his vocal organs from a lower primate who was 
also an ancestor of these apes, and it may be that the gibbon 
still retains these organs in part, but that they have degen- 
erated in the higher anthropoid apes. However, whatever 
the course of evolution may have been, it is evident that man 
has the best vocal organs, with certain birds ranking next. 
But the possession of well-developed vocal organs was 
not sufficient to insure the appearance of the highest mode 
of communication ; namely, language. For this to appear 
a high development of the cerebral hemispheres of the brain 
was necessary. The birds lacked this, and so failed to 
develop language. Whether the anthropoid apes could 
evolve a language if they possessed well-developed vocal 
organs, it is hard to say. Hence it is that communication 
by sounds by all animals but man is largely by means of 
emotional cries which do not convey any specific meaning, 
but which induce sympathetically similar states of feeling 
which lead to certain modes of behavior. Whether there 
is any other form of communication by sound outside of 
human language, it is hard to say. Certainly there is 
nothing in the way of the communication of abstract con- 
cepts, but it may be that some of the higher species use a 
few sounds which have definite meanings. 



The Factors of Social Evolution 411 

By means of communication and of imitation there is 
transmitted from one generation to another what is usually 
called tradition ; that is to say, modes of behavior and some- 
times, possibly even among animals other than man, in- 
formation as to conditions and events. It is evident that 
the amount of tradition which can be transmitted will 
depend upon the strength of the tendency to imitate and 
the abiHty to communicate. Furthermore, it is evident 
that the extent to which the benefits of experience and 
learning can be conserved and utiHzed will depend upon 
the extent to which tradition is transmitted. So that in 
this respect, also, man has the advantage over all other 
animals partly because of his great imitative capacities, 
not only in the form of organic imitation, but also to a high 
degree in the form of inteUigent and to a much lesser degree 
in the form of reflective or rational imitation. But his 
principal advantage Hes in his abiHty to communicate by 
means of language. It is frequently said with a large 
measure of truth that language is the principal distinction 
between man and the other animals, and this is so largely 
because by means of language man can conserve and trans- 
mit a much larger part of his experience than can any other 
animal without it. 

There are a few phenomena connected with the horde 
which I wish now to discuss briefly, since they are apparently 
due to the forces which have been described. The first is 
the formation of categories among certain species. That 
is to say, the horde is divided up in some way and the di- 
visions are distinguished and sometimes separated from 
each other. The division is in general according to sex or 
according to age. Certain kinds of fish segregate according 



412 The Science of Human Behavior 

to sex and sometimes according to age.^ It is said that 
roaches when they ascend rivers are separated into groups 
which are composed alternately of males and of females. 
It has been observed that when the salmon ascend rivers, 
the females go before the males, with the older individuals 
at the head of the troop and the younger ones behind. It 
is said that certain kind of eels that move from one pond 
or lake to another are often found segregated according to 
sex in different bodies of water. 

This formation of categories is to be found among certain 
birds. Perhaps the most striking case is that of the penguin. 
Flocks of these birds have definite places of abode where this 
segregation takes place. Here the flock separates into the 
young, the male adults, the female adults that are hatching 
eggs, and those that are not doing so. This formation of 
categories is also to be found among certain mammals. 
The North American bison were usually found in herds of 
males and herds of females with their young. Among the 
cetaceans the narwhals are said to Hve in herds of fifteen to 
twenty individuals which are always of the same sex. In 
certain herbivorous species, among which are to be found spe- 
cies of sheep, goats, horses, etc., at the season of the rut 
each of the older males gathers several females around 
him and then keeps the young males away from this 
family group. The young males then form groups by 
themselves. Among the primates it has been observed 
that when a troop of gibbons is traveling, the young are 
carried, the males by adult males and the females by their 
mothers. Among the gorillas troops of about five young 
gorillas are found together, but, as has been stated, these 

^ Cf. R. Petrucci, Originc polyphylHique des soci6t6s animaUs, Part III, chap. a. 



The Factors of Social Evolution 413 

troops are broken up when they become old enough to pair. 
A considerable diversity of phenomena is to be found under 
the head of the formation of categories, but I have not the 
space to describe them fully here. I wish, however, to 
discuss briefly the causes of these phenomena. 

Petrucci states his theory as to the cause of these phe- 
nomena in the following passage, which I will not attempt 
to translate on account of its idiomatic style: "II est 
facile de voir que la formation des categories, qui s'applique 
aux jeunes ou aux adultes, surgit ici comme une modalite 
particuliere de la tendance associative au sein du troupeau 
qui ne constitue une modaUte generale. C'est la recherche 
des semblables. On va voir qu'elle pent prendre un ca- 
ractere plus general." ^ He therefore attributes these phe- 
nomena to an associative tendency by which he seems 
to mean a gregarious instinct. I have already discussed the 
reasons for questioning the existence of a gregarious in- 
stinct. For my part, I do not know how to explain these 
phenomena. And indeed Petrucci himself confesses^ his 
inability to explain certain of these phenomena which ap- 
pear among men. It is quite possible, however, that, as he 
suggests, the greater degree of similarity between the mem- 
bers of the same sex may have something to do with it, and 
the same would be true as between the young and adults. 
Furthermore, there seems to be a certain degree of antipathy 
between the two sexes which displays itself with consider- 
able force even among men. This antipathy is at times 
overcome by the sexual instinct, but in many species this 
manifests itself only at the time of the rut, and at other 
times the sexes may be kept separate by this antipathy. 
1 op. cit., p. 79. ' op. cit., p. 89. 



414 The Science of Human Behavior 

Among men the rut seems to have disappeared, and the 
sexual instinct manifests itself with about the same strength 
at all seasons of the year, so that it probably acts as a re- 
straint upon this antipathy at all times. As between the 
adults and the young, sexual jealousy sometimes acts as a 
barrier between the adults and the adolescent males. These 
are but a few suggestions as to the possible causes of the 
formation of categories. As a matter of fact, there are in 
all probabiHty many causes for these phenomena, and the 
causes in each case vary somewhat from those in every other 
case. Though there are a considerable number of cases of 
the formation of categories in the whole animal world, and 
these cases appear, as we have seen, in three different classes 
of the vertebrates, yet the majority of the species in these 
classes do not display this phenomenon, while, so far as I 
know, it is not found at all among the amphibians and rep- 
tiles. So that it is probably due in each case to a rather 
pecuKar combination of forces which we cannot now ex- 
plain. Among primitive men it manifests itself in the sep- 
aration of the sexes in men's and women's houses, in the 
isolation of pregnant women, etc. Magical and religious 
reasons are usually given for the rules enforcing these cus- 
toms, and they are undoubtedly due in part to the growth of 
magical and rehgious ideas. But certain biological forces 
may be still more fundamental as causes. In modern 
society this phenomenon manifests itself in the segregation 
of the sexes in their club Hfe, etc., which is largely due to 
certain economic, poHtical, and social ideas and institutions, 
but may also be somewhat due to these biological forces. 
The next phenomenon which I wish to discuss is the 
meeting place or place of rendezvous. Many species of 



The Factors of Social Evolution 415 

fish come to certain places each year to lay their eggs. The 
turtles of the Galapagos Islands lay their eggs each year at 
the same places on the shore. Many species of birds do the 
same thing. Many flocks of birds migrate each year to and 
fro between the same places. Many mammals have so- 
called rutting places where they gather each year for the 
males to fight for the females in their presence. Primi- 
tive men have such places of rendezvous for dances, reli- 
gious ceremonies, etc., as, for example, the places where 
the AustraHan natives hold their corroborees. These 
meeting places appear usually to be connected with the 
function of reproduction. They are probably used the 
first time either by accident, or because they happen to be 
favorably located or well suited for certain purposes. Then 
the custom of using the same place becomes established 
and is transmitted by tradition from one generation to 
another. The existence of the place of rendezvous is then 
an indication of social life, and, though so frequently con- 
nected with reproduction, is probably always indicative of a 
social Hfe broader than that of the family. Furthermore, it 
marks one of the starting points for the evolution of the 
right of property, for these animals display a proprietary 
feeling with regard to these places and drive away all 
intruders. 

I wish to speak next of the phenomenon of leadership 
which sometimes plays an important part in the life of the 
horde. Wherever leadership exists it acts as a powerful 
force to bind together the members of a social group. The 
domination of the young by their parents may seem a case 
of leadership, but it is a Uttle different from leadership in the 
horde, since it is due to the weakness and helplessness of the 



416 The Science of Human Behavior 

young during infancy. Leadership in the horde may, how- 
ever, be due to superior strength, since in many species the 
leadership is determined by many combats among the males. 
In other cases the leadership may be attained as a result of 
initiativeness and originality. Frequently the leader is 
an old male, but he is not necessarily the leader because he 
is old, but because after having won the leadership when 
younger he has retained it through custom and tradition. 
Cases have been observed where an old female was the leader 
of a herd or pack. I do not know whether in these cases the 
position had been won by physical strength or as a result 
of the possession of certain mental qualities. It is doubtful 
if a young female is ever the leader of an animal group. 
But it is a physiological fact that in all the higher species the 
old female acquires some of the characteristics of the male. 
These characteristics make it possible for her to become the 
leader. The younger female is hampered by her repro- 
ductive functions from playing this part, as well as lacking 
the necessary physical and mental characteristics. These 
phenomena of leadership display themselves among the 
young at play among primitive peoples. Most of them 
appear among civilized men as well, but under somewhat 
dijQEerent forms. 

Theories of Social Evolution 

I have now completed this brief comparative study of the 
fundamental types of association and their origins. Though 
it has been a wholly inadequate treatment of this great 
subject, it has, I beheve, to say the least, revealed the com- 
plexity of the forces which have been at work in social 
evolution. I wish, therefore, before ending this chapter to 



The Factors of Social Evolution 417 

discuss briefly and critically some of the theories of the 
origin and nature of society which have been formulated. 
This discussion will show that each of these theories has 
been based upon only one of the groups of forces which 
have been at work in social evolution, and has therefore 
been inadequate. 

The first theory I refer to is that of the instinctive origin 
and nature of society. As might be expected, this theory 
seems to be held by most of those who believe in the exist- 
ence of a gregarious instinct. Two recent representatives 
of this theory are McDougall and Petrucci. McDougall, 
while he may not expressly avow this theory at any one 
point, seems to be trying in his recent treatise on social 
psychology to explain human society entirely on the basis 
of instinct and of emotion, which he regards as the affective 
aspect of instinct. Petrucci also may not expressly avow 
this theory. But, as we have seen, he believes in the exist- 
ence of an associative tendency, by which he seems to mean 
a gregarious instinct, and his constant effort is to interpret as 
far as possible all social phenomena in terms of this tendency. 

We have seen the important part played by several 
instincts in social evolution. The family is perhaps wholly 
instinctive in its origin. But the horde certainly is not. 
Or even if we were to admit that it was, its evolution has 
depended upon the introduction and constantly increasing 
importance of certain intelligent forces, such as imitation, 
recognition, communication, leadership, etc. And the 
horde is, in the long run, of most importance for social evolu- 
tion, for the family is by its nature necessarily a social group 
very limited in its numbers and very exclusive in its charac- 
ter. It is only in the larger size, greater diversity, and 
2e 



418 The Science of Human Behavior 

broader interests of the larger social groups that we can 
hope to find the higher stages of social evolution, and here 
we find inteUigence playing a constantly increasing part. 
So that it is indeed surprising to find the highest form of 
society, namely, human society, interpreted so exclusively 
in terms of instinct. 

The next theory is that of the emotional origin of society. 
Most of those who have held this theory have contended 
that society originated from sympathy. An older repre- 
sentative of this theory was Adam Smith, who, however, 
wavered somewhat between this theory and the theory that 
society originated from cooperation or mutual aid. Perhaps 
the most elaborate statement of the theory has been made 
by Sutherland in his treatise on the Origin and Growth 
of the Moral Instinct. In this voluminous work he en- 
deavors to prove with a wealth of illustration that all 
social phenomena are the outgrowth of sympathetic emotions 
which arise from parental care. The extreme to which he 
carries this theory can best be indicated by means of a few 
quotations. For example, he speaks as follows of the part 
played by sympathy : "It will be subsequently perceived 
that parental sympathy is the basis of all other sympathy, 
and that sympathy in general is the ultimate basis of all 
moral feeling." ^ And again he says: "The sympathetic 
type is thus the one which is more and more distinctly 
emergent as we ascend in the animal scale; for not only 
does an increasing parental care give to a species some 
preference over competitive types; but an increasing con- 
jugal stability also allies itself with this parental care, to 
form the home circle, and to build up the family wherein, 

» Vol. I, p. 156. 



The Factors of Social Evolution 419 

as we shall see, is the birthplace of all moral relations." ^ 
Earlier in this chapter I have shown quite fully the part 
played by parental care in social evolution, so that I cannot 
be accused of ignoring its importance. But this chapter has 
also shown that the family could not possibly be ^'the birth- 
place of all moral relations, " as Sutherland says, and by the 
word "moral" here he evidently means practically the same 
thing as ^ ' social. ' ' On the contrary, certain moral and social 
relations could arise only in the larger social groups, and the 
family is positively antagonistic to some of these relations. 
Indeed, we have seen that the higher types of society cannot 
evolve from the family, which is too narrow and exclusive in 
its character, but must arise from these wider forms of as- 
sociation. 

Those who hold this theory that society can be accoimted 
for entirely on the basis of sympathy usually have little or 
nothing to say about the part played by instinct. It is 
true that Sutherland calls his book a treatise on the moral 
instinct. But he scarcely mentions instinct throughout the 
book, and in his labored exposition of the nature of emotion 
gives no suggestion that the two are related to each other. 
And yet we have seen in earlier chapters that some emotions 
at any rate are caused by instinctive actions and that all 
emotions result either from some form of behavior or from 
internal physiological processes. So that it is impossible 
to discuss emotion apart from behavior, and if the emotions 
which play a part in association are caused by instincts, then 
the emotional theory of the origin of society could be as- 
similated with the instinctive theory, for the instincts would 
be the ultimate causes of association. 

1 Vol. I, p. 291. 



420 The Science of Human Behavior 

Let us now turn to the so-called intellectualistic theories of 
the nature of society which give a large place to intelligence 
in the higher forms of association. First, I will speak of 
Giddings' theory of the consciousness of kind as "the origi- 
nal and elementary subjective fact in society." He defines 
this as "a state of consciousness in which any being, whether 
low or high in the scale of Hfe, recognizes another conscious 
being as of Hke kind with itself." ^ If then this state of 
consciousness is a form of recognition, it must be an intelli- 
gent factor and his theory an intellectualistic one. However, 
on the very next page he remarks that "in its widest ex- 
tension the consciousness of kind marks off the animate 
from the inanimate," which remark seems to intimate that 
it is coextensive with animate matter, in which case it cer- 
tainly is not an intelligent factor, since, as we have seen, 
intelligence is not coextensive with all animate matter. 
However, he may not intend to imply this, for in the preface 
to the third edition he states that his theory was derived 
in part from Adam Smith's theory that society originated 
from sympathy, which was set forth in Smith's Theory of 
Moral Sentiments, but that his theory includes an element 
of perception. Thus he says: "I could not adopt Adam 
Smith's word ^sympathy,' or the famihar term 'fellow- 
feehng,' as a name for the primary social phenomenon, 
because it was necessary to recognize the element of per- 
ception. . . . The consciousness of kind, then, as I con- 
ceive it, is at once perception and feeling." Giddings' 
theory therefore recognizes an emotional factor and an 
intelligent factor, with nothing said as to instinct. 

Another theory is that society originates from mutual 

» F. H. Giddings, The Principles of Sociology, New York, xgog, p. 17. 



The Factors of Social Evolution 421 

aid. Adam Smith inclined towards this theory in his 
Wealth of Nations^ though, as we have seen, elsewhere 
he inclined towards the sympathetic theory. Kropotkin 
has emphasized the importance of mutual aid in his trea- 
tise on this subject, in which he contends that it has been 
the most important factor not only in social evolution, 
but also apparently he would have us think in the whole of 
organic evolution. It is evident that conscious mutual aid 
as distinguished from the unconscious physiological division 
of labor which results from pol3anorphism is a highly in- 
teUigent phenomenon and does not appear until long after 
the beginning of social evolution. 

There are various other intellectualistic theories, such as 
Tarde's theory that imitation has been the principal factor 
in social evolution, and Durkheim's theory that the influence 
of the many upon the individual has been the principal 
factor. But I beheve that I have illustrated sufficiently the 
different types of theories and have not the space to dis- 
cuss more of them.^ All of the writers whose theories have 
been mentioned above — namely, McDougall, Petrucci, 
Adam Smith, Sutherland, Giddings, Kropotkin, Tarde, 
and Durkheim, — have made important contributions to 
the analysis of social evolution, but it is evident that all of 
their theories are too unilateral and do not include all the 
factors in social evolution. 

^I have not discussed the theory of social evolution of the dean of American 
sociologists, Lester F. Ward, because it is difficult to classify his theory. He seems 
to regard feeling as the principal factor in social evolution, though he gives much 
weight to intellect also, but has little to say of instinct. (See his Pure Sociology, New 
York, 1903, especially chapters XII and XV, and Psychic Factors of Civilization, 
Boston, 1893.) 



CHAPTER XXI 

CONCLUSION 

Summary of the preceding chapters, 422. — This book furnishes 
a basis for the study of the more complex human mental and social 
phenomena, 424. 

We have now completed this survey of the evolution of 
behavior. The treatment has necessarily been brief, and a 
vast amount of data bearing on all the phenomena dis- 
cussed has been omitted. But the attempt has been made 
to describe the principal stages in the evolution of behavior 
and the principal types of behavior. Let us review briefly 
the subjects discussed. 

In all study of behavior it is necessary to begin with the 
structural form upon which is based the action-system 
which determines the behavior. The first part of the book 
was therefore devoted to the morphological evolution in the 
course of which were evolved the structural forms which 
determine behavior. Then were studied the direct reactions 
of the lower animals to external forces. But when the nerv- 
ous system developed, these reactions became more or less 
indirect, so that we find new types of behavior appearing. 
The fundamental type of behavior determined by the nerv- 
ous system is the reflex action »^ These actions become in 
course of time combined into complex forms which are 
usually called instincts. Because of the complex character 
of many of these instincts and the difiiculty of analyzing 
their mechanism, there has been a tendency on the part of 

422 



Conclusion 4£3 

many writers in the past, and the same is still true even 
to-day on the part of some, to regard instinct as a form of 
behavior which is not mechanically determined. The at- 
tempt has therefore been made in this book to render the 
conception of instinct more precise than it has yet been 
stated by any other writer on the subject. 

We then pass to intelligent behavior, the appearance of 
which marks a new stage in the evolution of behavior. The 
previous forms of behavior are inherited in the sense that 
animals are predetermined to manifest them when the ap- 
propriate stimuH are applied. But inteUigent behavior is 
not inherited in this sense, but is determined by individual 
experience. A structural form which is capable of benefit- 
ing by experience must be inherited if intelligent behavior is 
to make its appearance, but the form it is to take will de- 
pend largely upon individual experience. As in the case of 
instinct, the attempt has been made in this book to make 
the conception of intelligence more precise than it has 
hitherto been stated by other writers on the subject. Con- 
sciousness and mind are also discussed, but it is still very 
difficult to make very precise our conceptions of these 
phenomena. They must, however, be discussed in such a 
book as this, because of the part they play in the determina- 
tion of behavior and also because it is possible that they 
can be reduced to a certain extent, if not entirely, to terms 
of behavior. In the latter part of the book are discussed 
the nature and evolution of social behavior in which we 
find combined in the most complex fashion the types of 
behavior already discussed. 

It has been impossible within the limits of this book even 
to touch upon many complex phenomena which have 



424 The Science of Human Behavior 

evolved in the course of human social evolution and which 
either are forms of behavior or play an important part in 
determining human behavior. Among these are aesthetic, 
moral, religious, economic, and political phenomena. But I 
believe that the necessary basis for the study and analysis of 
these phenomena has been furnished in large part, for these 
phenomena are made up of the fundamental types of be- 
havior and of mental phenomena which have been de- 
scribed in this book. Much writing on these subjects has 
been of little or no value because the writers have not 
had this basis. This book, therefore, furnishes a basis for 
the study of human mental and social evolution and also 
for the study of society as it now exists. 



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INDEX 



Acquisitiveness, 242. 

Action system, the, 126 ff., 269. 

Adaptation, 26, 146, 213 £f., 232 ff., 

263. 
Affection, 244, 304. 
Allelomorph, 55 ff., 61, 67. 
AUotropism, 13. 
Amoeba, 118 ff. 
Amphibian, 157, 370 ff. 
Amphimixis, 43. 
Amphioxus, 329. 
Anemotropism, 116. 
Angell, J. R., 278, 313. 
Anger, 302. 
Ant, 106, 268, 338 ff. 
Anthropoidea, 384 ff. 
Anthropology, 72 ff., 172. 
Ape, 280, 309, 333 ff., 357, 38s ff. 
Aphid, 349 ff. 
Arachnida, 351. 
Arm, 270 ff., 272. 
Arthropoda, 351. 
Aspredo, 367. 

Association, 327 ff., 355, 364 ff., 390 ff. 
Association area, 181 ff., 211, 265, 270 ff., 

272, 274, 280, 288, 290, 359 ff. 
Associative memory, 260 ff., 288. 
Atom, 8. 
Attention, 290 ff. 
Aye- Aye, 384 ff. 



B 



Baboon, 385. 

Bacteria, 120 ff. 

Badger, 381, 382. 

Bain, A., 295. 

Baldwin, J. M., 134, 225, 277, 279, 281 

282, 295, 297. 
Barker, L. F., 178. 
Barotaxis, 113 ff. 
Bat, 379. 
Bateson, W., 46 ff., 55 ff., 61, 63, 71. 



Batrachia, 370 ff. 

Beaver, 380. 

Bee, 268, 294, 338 ff. 

Behavior, i ff., 198, 256 ff., 422 ff. 

animal, i, 74, 76 ff., 117 ff. 

definition of, i. 

human, 3. 
Bergson, H. 266 ff. 
Bethe, A., 261. 
Binet, A., 80, 278, 360. 
Biogen, 37. 

Biology, 2, 68 ff., 75 ff., 172. 
Biophor, 39, 53. 

Bird, 168, 233, 268, 2,zi, 345> 372 ff. 
Bison, 253, 412. 
Bohn, G., 82, 96, 268. 
Bolton, J. S. 185, 193. 
Brain, 157, 159, 163, 166 ff., 175 ff., 195, 
228 ff., 270 ff., 302 ff., 359 ff., 389. 
Brandt, 360. 
Brehm, A. E., 364. 
Brooding, 373. 
Buhler, 278. 



Calkins, Mary W., 314, 319 ff. 

Campbell, A. W., 184. 

Carbon, 13. 

Carnivora, 333, 381 ff., 391. 

Cassowary, 373. 

Cat, 190, 191, 381, 382, 383. 

Categories, 411 ff. 

Caterpillar, 342. 

Cebidce, 385. 

Cell, the organic, 16 ff., 49, 328. 

Central nervous system, 156 ff., 171, 

231, 262 ff., 288, 322, 336. 
Cercopithecidcs, 385. 
CerebeUum, 167, 168 ff., 228 ff. 
Cerebral localization, 175 ff. 
Cerebrum, 159, 167, 168, 172 ff., 176 ff., 

228 ff., 265, 270. 
Cetacea, 379. 
Chain instinct, 230 ff., 399 ff. 



437 



438 



Index 



Characters, 

acquired, 27, 30 ff., 216, 217, 286, 337. 

degeneration of, 31, 40 ff. 
Chemistry, 7. 

Chemotropism, 109 ff., 335. 
Chimpanzee, 173, 385 ff., 394. 
Chiroptera, 379. 
Chromatin, 22. 
Chromosome, 66 ff. 
Chromotropism, 102 ff. 
Circulation, 20. 
Civet, 381. 
Claparede, E., 316. 
CleanUness, 242. 
Ccelenterata, 268. 
Colony, 328 ff., 340, 345, 356. 
Commensalism, 342, 351. 
Common path, the, 160 ff., 212. 
Communication, 337, 362, 375, 409 ff. 
Concept, 278. 
Conduct, 2. 

Conjugal relation, the, 378, 399 ff. 
Consciousness, 130, 134, 214 ff., 233, 257, 

260, 273, 275, 280, 281 ff., 322 ff. 
Consciousness of kind, 420. 
Constructiveness, 242. 
Contact irritability, 113 ff. 
Cooperation, 254, 335, 363, 376. 
Copulation, 114. 
Corpuscle, 9. 
Correns, 55. 
Corroboree, 415. 
Cortex, 178 ff., 181, 1845., 196, 229, 

263 ff., 270. 
Cranium, 175, 271. 
Crayfish, 268. 
Crocodile, 371. 
Crustacean, 268, 293, 352. 
Crystals, 16, 25, 29. 
Cunningham, D. J., 271, 272 
Curiosity, 242. 
Cytoplasm, 22. 



D 



Darwin, Chas., 29, 32 ff., 40 ff., 53, 63, 
6s, 70, 238, 301. 393, 405- 

Davenport, C. B., 58, 82 ff., 84, 85, 90, 
92, 100, 102, 107, 113 ff., 116, 117. 

Deciduate, 378 ff. 

Deer, 380. 

Delage, 39. 

Deniker, J., 173. 

Determinant, 39, 40 ff. 



Disease, fimctional, iqs ff. 

organic, 195 ff. 
Disgust, 302. 
Division of labor, 254. 
Dog, 170, 249, 302, 309, 381, 382, 383. 
Domestication, 382 ff. 
Duckbill, 377. 
Dujardin, 360. 
Durkheim, E., 421. 



Earthworm, 96, 105 ff. 

Echidna, 377. 

Echinodermata, 293. 

Ectoparasite, 354 ff. 

Edentata, 379. 

Edinger, L., 229, 270. 

Education, 273. 

Eimer, T., 27 ff., 34, 45. 

Electricity, 9, 112, 119, 123. 

Electrolyte, 9. 

Electron, 9. 

Electrotropism, 112. 

Elephant, 380. 

Emery, 46. 

Emotion, 219, 220 ff., 286, 299 ff., 372 ff., 

406 ff., 418 ff. 
Emu, 373. 

Emulation, 241, 251. 
Energy, 7. 
Entoparasite, 354 ff. 
Environment, 337, 395. 
Envy, 244. 
Escherich, 351. 
Espinas, A., 328, 403, 405. 
Ether, 7, 99. 
Euglena viridis, 96 ff. 
Evolution, organic, 12, 45, 134, 136, 

318, 331 ff. 
Experience, 210, 257 ff., 315. 
Eye, 214. 



Fabre, J. H., 233. 
Face, 271, 272. 
Facilitation, 160. 

Family, 336, 340, 343 ff-. 374 ff-. 399 ff- 
Fear, 242, 302, 304. 
FeeHng, 219, 261, 295 ff., 316 ff. 
Finch, 374. 

Fish, IIS, 157, 268, 294, 330, 333, 336, 
365 ff. 



Index 



439 



Fission, 21 ff., 335. 

Flechsig, 181, 182, 185, 270, 271. 

Flight, 244. 

Flogel, 360. 

Flounder, 294. 

Fly, 294, 355- 

Folsom, J. W., 199. 

Forel, A., 261, 268, 360. 

Formicida, 345, 346, 356. 

Fossil, 337, 364. 

Franz, S. I., 176, 189 £E. 

Frog, 370. 

G 

Gall, 179. 

Galton, F., 39, 46, 51, 60 ff., 73, 380. 
Galvanotropism, 112. 
Gemmules, 35, 39, 53. 
Geotropism, 107 ff. 
Germ cell, 22 ff., 35 ff., 39 ff., 53 ff. 
Germ plasm, 38 ff., 341. 
Gestation, 384, 387. 
Gibbon, the, 385 ff., 391. 
Giddings, F. H., 420, 421. 
Gland, 144, 149 ff. 
Goltz, F., 304. 

Gorilla, 173, 385 ff., 391, 394. 
Gravity, 107 ff., 123. 
-sMjregariousness, 252 ff., 331, 380 ff., 385, 
391, 395 ff. 
Groos, K., 250. 
Gulick, 34. 
Gynandromorph, 67. 



H 



Habit, 216, 217, 254 ff., 264, 286, 302. 
Haeckel, E., 39, 80. 
Hand, 270 ff., 272. 
Hapalidcs, 385. 
Harvesting ant, 347. 
Hawk, 254, 393. 
Head, 270. 
Heart, 202, 
Heat, 116, 120, 123. 
Heliotropism, see phototropism. 
Helmholtz, H., 214. 
Eerbivora, 333. 
Heredity, see inheritance. 
Herrick, C. J., 264, 289, 314, 315, 317. 
Heterogenesis, 24, 45 ff. 
Heterozygote, 56 ff., 61. 
Hobhouse, L. T., 140, 141, 203, 204, 218, 
308, 310, 312. 



Holleman, A. F., 113. 

Holmes, S. J., 98, 261, 268. 

Holt, E. B., 94. 

HominidcB, 385. 

Homozygote, 56 ff., 61. 

Horde, 387, 404 ff., 411 ff. 

Horse, 380. 

Howell, W. H., 155, 178, 202. 

Hunting ant, 346. 

Hunting instinct, 242, 249, 250, 346. 

Huxley, T. H., 287. 

Hybrid, 55 ff., 73. 

Hydrogen, 8, 14. 

Hydrotropism, 116. 

Hymenoptera, 340, 360. 



Id, 39. 

Idea, 180 ff., 270, 291, 311, 316 ff., 337. 

Ideo-motor, 246 ff., 275. 

Image, 211, 274 ff., 291, 311. 

Imageless thought, 278 ff. 

Imitation, 212, 241, 246 ff., 251, 337, 355, 

359, 362 ff., 375, 407. 
Impulsive instinct, 230 ff., 240 ff. 
Infusoria, 268, 328. 
Inheritance, 60 ff., 204, 208, 216, 332, 

400. 
Inhibition, 160, 211, 212, 275 ff., 311 ff. 
Innate tendencies, 244, 245 ff. 
Insect, III, 233, 268, 294, 338 ff. 
Insectivora, 379. 
Instinct, 197 ff., 266 ff., 286, 300, 395 ff., 

417 flf. 
a new definition of, 226. 
Integration, 161 ff., 205, 206, 209, 251, 

263, 266, 308, 311. 
Intellect, see intelligence. 
Intelligence, 212, 229 ff., 238 ff., 256 ff., 

289, 314 ff-, 322 ff., 337, 338, 346, 

359 ff., 383, 407 ff., 420 ff. 
Introspection, 257, 278, 294. 
Invertebrate, 268 ff., 288, 333, 338, 363. 
Ion, 9. 

Irritability, 79 ff., 138. 
Isomerism, 13. 



Jackal, 392. 

James, W., 207, 211, 220 ff., 223 ff., 238, 

240 ff., 283, 300, 305. 
Jealousy, 376, 382, 403, 414. 



440 



Index 



Jennings, H. S., 76, 77, 78, 83 ff., 85, 
9Sfif.,*i04, iioff., IIS, ii8ff., i38ff., 
259, 284 ff. 

Johannsen, W., 64. 

Johnston, J. B., 162, 170, 171, 174, 178, 
181 ff., 192, 271. 

Jones, H. C., 11. 

Judd; C. H., 316 ff. 



K 



Kellogg, V. L., 71. 
Kelvin, Lord, 37. 
Kenyon, 360. 
Knowledge, 266 ff., 

nature of, 4, 325 ff. 
von KoUiker, 46. 
Korschinsky, 46. 

von Krafft-Ebing, R., 194, 195 ff. 
Kropotkin, P., 404 ff., 421. 



Lamarck, J. B., 30 ff., 36, 45. 

Lane, A. C, 18. 

Lange, 220 ff., 300. 

Language, 409 ff. 

Larva, 342 ff., 352, 355. 

Leadership, 363, 415 ff. 

Learning, 261, 264, 273 ff., 315, 363. 

Le Dantec, F., 39, 54. 

Lee, F. S., 94- 

Lemur, 333, 384 ff. 

Lemuroidea, 384 ff. 

Lewes, G. H., 216, 286. 

Leydig, 360. 

Light, 88 ff., 119. 

Lion, 254. 

Lizard, 371. 

Lodge, Oliver, 10. 

Loeb, J., 22, 54, 78, 81 ff., 89 ff., 92, 96, 
100 ff., 103, 106, 108, 109 ff., 112, 
138 ff., 151, 198 ff., 260 ff., 268, 288, 
294, 314. 

Lubbock, J., 233, 268. 



M 



Macaque, 385. 

Magic, 414. 

Mammal, 157, 170, 268, 280, 295, 333, 

34S» 364, 372, 376 ff. 
Mammary glands, 377 ff., 384. 
Man, 280, 364, 38s, 387 ff. 



Marshall, H. R., 245. 

Marsupial, 333, 377 ff. 

Mast, S. O., 88. 

Maternal care, 203, 249, 367 ff., 373, 384 ff. 

Matter, characteristics of, 7, 282, 285, 

287, 323 ff. 
organic, 7, 12 ff., 79 ff., 245, 274, 285, 

287. 
McCabe, J., 18, 272. 
McDougall, W., 140, 160, 163, 212, 218 

ff., 244, 322, 417, 421. 
Medulla oblongata, 167, 228. 
Meeting places, 414 ff. 
Memory, 216, 311. 
Mendel, G., 55 ff., 64, 67, 71 ff. 
Metabolism, 17, 20, 100, 121. 
Metaphyta, 24. 
Metazoa, 24, 118 ff., 127 ff., 138, 148,328, 

335, 336. 
Meyer, Max, 298, 316. 
Micella, 39. 

Micromerism, 39, 53 ff. 
Mills, 184, 185, 187. 
Mind, 214 ff., 257, 281, 286, 294, 321 ff., 

328 ff., 348, 355, 359, 363, 389. 
Minot, C. S., 317. 
Mitosis, 21, 49, 
Modesty, 242. 
Molecule, 8. 
MoUusk, 328. 
Monism, 283. 
Monkey, 190, 191, 280. 
Monogamy, 375, 387. 
Monotreme, ^iSi- 
Montague, W. P., 314, 325. 
Morgan, C. L., 134, 202, 203, 214, 224, 

225, 255, 261, 302, 303, 315, 348, 

392, 404 ff- 
Morgan, T. H., 52, 53, 65, 106, 199. 
Moth, 107. 
Mott, F. W., 229. 
Mouth, 271, 272. 
Mulatto, 58. 

Multiple personality, 309 ff. 
Muscle, 144, 148 ff., 202. 
Mutation, 51 ff., 58 ff., 207, 208. 
Mutual aid, 254, 421, 
MyrmecophiUsm, 351 ff. 
Myrmecoxene, 352. 



N 



Nageli, C, 25 ff., 39, 45. 
Negro, 58. 



Index 



441 



Neo-Darwinism, 38. 

Neo-Lamarckism, 28, 51 ff. 

Nerve, 137 ff., 201 ff., 227 ff., 304 ff. 

316, 336, 384. 
Nest, 232, 233, 338, 342 ff., 347, 368. 
Neuromere, 163, 167. 
Neurone, 154 ff., 275 ff. 
Newt, 370. 
Nitrogen, 14. 
Nondeciduate, 378 ff. 
Norman, W. W., 292 ff. 
Nuptial flight, 343. 

O 

(Enothera Lamarckiana, 51 ff. 

Opossum, 377. 

Optimum, the, 104. 

Orang-utan, 173, 385 ff. 

Ornithorynchus, 377. 

Orthogenesis, 24 ff., 43, 45, 48. 

Osbom, H. F., 134- 

Ostrich, 373. 

Otolith, 109. 

Ova, 23, 67, IIS ff-> 366 ff. 

Oviparity, 366, 373. 

Owl, 374. 

Ox, 380. 

Oxygen, 8, 13, 121. 

Ozone, 13. 



Pagano, 229. 

Pain, 27s ff., 284 ff., 291 ff. 

Pangene, 39. 

Pangenesis, 35. 

Panmixia, 42. 

Paramecium, iii ff., 121 ff., 284, 289. 

Parasitism, 342, 351, 355 ff. 

Parental care, 203, 243, 253, 336, 344, 

348, 350, 367 ff-, 370 ff., 374, 397 fi- 
Parental instincts, 337, 342 ff., 364 ff., 

397 ff. 
Parker, G. H., 103, 140, 143 ff., 147 ff. 

202. 
Parrot, 374. 
Parthogenesis, 43. 
Pastoral ant, 346, 347 ff., 357. 
Paternal care, 367 ff., 373. 
Pearson, K., 35, 58, 61, 73. 
Peckham, Mr. and Mrs., 233, 268. 
Penguin, 412. 
Periodic law, 8. 



Perrier, E., 329. 

Personality, 307 ff. 

Petrucci, R., 329 ff., 332 ff., 388, 412, 
413, 417, 421. 

Peuplade, the, 403 ff. 

Pheasant, 373. 

Philoprogenitive instincts, see reproduc- 
tive instincts. 

Photopathy, 92 ff. 

Phototaxis, see phototropism. 

Phototropism, 88 ff. 

Phrenology, 175, 179, 180. 

Physics, 7. 

Physiognomy, 175. 

Physiological division of labor, 328, 335, 
339 ff-, 363. 

Physiological state, 131 ff., 136. 

Physiological xmit, 39. 

Pigeon, 233, 373. 

Placentalia, 378. 

Planarian, 96, 106. 

Plastidxile, 39. 

Platypus, 377. 

Play, 242, 248 ff. 

Pleasure, 275 ff., 284 ff., 291 ff. 

Polyandry, 387, 401. 

Polygyny, 385, 387, 4oi- 

Polymorphism, 339 ff., 363. 

Polyp, 328. 

Polyphyletism, 391 ff. 

Pons VaroUi, 167, 228. 

Porthesia chrysorrhcea, 106. 

Primate, 271, 272, 280, 333, 384 ff. 

Promiscviity, sexual, 387. 

Protophyta, 23. 

Protoplasm, 16 ff., 118 ff., i38ff., 146, 274. 

Protozoa, 118 ff., 127 ff., 138, 328. 

Psychology, 2, 3, 69 ff., 77 ff., 325 ff. 

Psycho-physical interactionism, 322. 

Psycho-physical paralleUsm, 278, 285 ff., 
321 ff. 

Pugnacity, 241 ff., 249, 251, 302. 

Pure lines, 64 ff. 



Queen ant, 343, 357, 358. 



R 



Rabbit, 380. 
Rabl-Ruckard, 360. 
Raccoon, 381, 382. 
Radioactivity, 10. 



442 



Index 



Radium, lo. 

Read, Carveth, 229, 233 ff. 

Reason, 198, 279 ff. 

Receptor, 164 ff., 171, 173, 280. 

Recognition, 337, 360 ff. 

Reenforcement, 211, 217, 275 ff., 305, 312, 

407 ff. 
Reflex, 128 ff., 140 ff., 159 ff-, 187, 191, 

197, 198 ff., 256, 259, 289, 330, 335. 
Regression, 62. 
Religion, 414. 

Reproduction, 21 ff., 335 ff. 
Reproductive instincts, 352 ff., 358, 363, 

397. 
Reptile, 157, 268, 333, 371 ff., 376. 
Repulsion, 244, 
Respiration, 20. 
Reversion, 59 ff. 
Rhea, 373. 
Rheotropism, 114 ff. 
Rhinoceros, 380. 
Richet, C, 79, 80. 
Rivalry, 241, 251. 
Rodentia, 333, 379. 
Romanes, G. J., 28, 34, 198, 201, 204, 

215 ff., 286, 315. 
Royce, J., 316, 320, 321, 323, 324, 325. 
Rut, the, 399, 412, 413, 414. 
Rutherford, E., 12, 323. 



von Sachs, J., 90, 91, 151. 

Salamander, 370. 

Salmon, 412. 

Santee, H. E., 178, 179, 183 ff., 192. 

Schiller, F., 248. 

Seal, 381, 382. 

Secretiveness, 242. 

Selection, 33 ff., 40 ff., 134, 213, 253, 383. 

Selenotropism, 89. 

Self-abasement, 244. 

Self-assertion, 244. 

Self-consciousness, 307 ff. 

Sensation, 180 ff., 274, 280, 290 ff. 

Sensori-motor, 225, 275. 

Sex, 6s ff., 335. 

Sexual dimorphism, 339. 

Sexual instinct, 210, 242 ff., 253, 336, 

337, 364 ff., 296 ff., 399 ff. 
Shame, 242. 
Shark, 294, 369. 
Sheep, 380 
Sherrington, C. S., 143 ff., 145 ff., 156, 



160, 161 ff., 163, 164 ff., 171, 173, 

202, 206, 302, 303, 304, 305. 
Shyness, 242. 
SimiidcB, 385, 391. 
Sirenia, 379. 

Slave-making ant, 357 ff. 
Smell, III, 361, 366. 
Smith, Adam, 418, 420, 421. 
Snake, 371. 
Snyder, Carl, 17, 18. 
Sociability, 242, 252 ff., 392. 
Society, 328 ff., 390 ff. 
Sociology, 2, 3, 69 ff. 
Sparrow, 374. 

Species, origin of, 23 ff., 45. 
Spencer, H., 14, 15, 39, 168, 171, 199 ff., 

202, 224, 248, 298, 301, 315. 
Spermatozoa, 23, 67, 115 ff., 366. 
Sphenodon, 373. 
Spiny anteater, 377. 
Spurzheim, 179. 
Stentor ccernleus, 95 ff. 
Stentor roeselii, 124 ff. 
Stereotropism, 113 ff., 370. 
Stickleback, 368. 
Stimuli, 85 ff., 132, 14s, 150 ff., 164 ff., 

210. 
Stirps, 39. 

Stout, G. F., 225, 278, 282, 297. 
Strasburger, E., 90. 
Stridulation, 362. 
Structure, 206 ff., 264, 269, 324. 
Struggle for existence, 33, 36, 41 ff., 213, 

392. 
Subatomicity, 9. 
Subconscious self, 310 ff. 
Sucking reflex, 203. 
Suggestion, 247, 336, 355, 359, 362 ff., 

375, 407. 
Sutherland, A., 366, 369, 398, 418, 419, 

421. 
Symbiosis, 347 ff. 

Symmetry, 27, 29, 47 ff., 93, 112, 269. 
Sympathy, 242, 247, 266 ff., 418 ff. 
Symphile, 352, 353 ff., 355. 
Synapse, 155 ff., 276. 
Synechthran, 352 ff., 355. 
Synoekete, 352, 353, 355- 



Tait, P. G., 37. 
Tarde, G., 421. 
Tarsius spectrum, 384 ff. 



Index 



443 



Taste, 111. 

Taxis, 84. 

Termite, 339, 357. 

Theories of social evolution, 416 ff. 

Thermotropism, 116. 

Thigmotropism, 113 ff. 

Thomson, J. A., 34, 35. 

Thorndike, E. L., 268, 276, 407. 

Thought, 277 ff. 

Tiger, 254, 392. 

Titchener, E. B., 278, 287, 321. 

Toad, 370. 

Tonotropism, 116. 

Tool, 271, 272. 

Torrey, H. B., 97 flf. 

Tortoise, 371. 

Tradition, 273, 337, 375, 411. 

Transient instincts, 213. 

Tropism, 81 fit., 88 fif., 136, 197, 198 ff ., 256, 

259, 284, 289, 330. 
Tschermak, 55. 
Turtle, 371. 



U 



Ungulata, 378, 380 ff., 391. 

Urea, 13. 

Utility for survival, 392. 



Variation, 32 ff., 36 ff., 40 ff., 46 ff., 68 ff., 

134, 213. 
Vascular or vasometer system, 300 ff., 

328, 372. 
Veblen, T., 252. 
Vertebrate, 156 ff., 268 ff., 288 ff., 294, 

295, 329, 333, 364 ff. 



Verworn, M., 17, 39, 84, 86 ff., 91, 113 

ff., 116, 117, 141 ff. 
Viscera, 300 ff. 
Vision, 105. 

Viviparity, 366 ff., 370. 
Volition, 311 ff. 
de Vries, H., 39, 46, 51 ff., 55, 59, 60, 

65. 

W 

Wagner, 34. 

Waldeyer, 154. 

Walrus, 381. 

Ward, J., 320. 

Ward, L. F., 421. 

Washburn, Margaret F., 81, 84, ii6. 

Wasmann, E., 268, 351, 361. 

Wasp, 233 ff., 268, 338 ff., 392. 

Weasel, 381, 382. 

Weismann, A., 38 ff., 53, 64, 341. 

Wheeler, W., M., 268, 294, 339 ff., 341, 

342, 344, 346, 347, 352, 354, 357, 360. 
Whetham, W. C. D., 10, 324. 
Whitman, C. O., 233. 
Wilder, H. H., 156. 
Will, 311 ff- 
Woodpecker, 374. 
Woodworth, R. S., 278. 
Worker ant, 341 ff., 343 ff. 
Workmanship, 252. 
Worm, 233, 293, 328. 
Writing, 271. 
Wxmdt, W., 153, 154, 160, 169, 171, 172, 

178, 180 ff., 278. 



Yerkes, R. M., 268, 325. 



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